Source file src/net/http/transport.go

Documentation: net/http

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // HTTP client implementation. See RFC 7230 through 7235.
     6  //
     7  // This is the low-level Transport implementation of RoundTripper.
     8  // The high-level interface is in client.go.
     9  
    10  package http
    11  
    12  import (
    13  	"bufio"
    14  	"compress/gzip"
    15  	"container/list"
    16  	"context"
    17  	"crypto/tls"
    18  	"errors"
    19  	"fmt"
    20  	"io"
    21  	"log"
    22  	"net"
    23  	"net/http/httptrace"
    24  	"net/textproto"
    25  	"net/url"
    26  	"os"
    27  	"reflect"
    28  	"strings"
    29  	"sync"
    30  	"sync/atomic"
    31  	"time"
    32  
    33  	"golang.org/x/net/http/httpguts"
    34  	"golang.org/x/net/http/httpproxy"
    35  )
    36  
    37  // DefaultTransport is the default implementation of Transport and is
    38  // used by DefaultClient. It establishes network connections as needed
    39  // and caches them for reuse by subsequent calls. It uses HTTP proxies
    40  // as directed by the $HTTP_PROXY and $NO_PROXY (or $http_proxy and
    41  // $no_proxy) environment variables.
    42  var DefaultTransport RoundTripper = &Transport{
    43  	Proxy: ProxyFromEnvironment,
    44  	DialContext: (&net.Dialer{
    45  		Timeout:   30 * time.Second,
    46  		KeepAlive: 30 * time.Second,
    47  		DualStack: true,
    48  	}).DialContext,
    49  	ForceAttemptHTTP2:     true,
    50  	MaxIdleConns:          100,
    51  	IdleConnTimeout:       90 * time.Second,
    52  	TLSHandshakeTimeout:   10 * time.Second,
    53  	ExpectContinueTimeout: 1 * time.Second,
    54  }
    55  
    56  // DefaultMaxIdleConnsPerHost is the default value of Transport's
    57  // MaxIdleConnsPerHost.
    58  const DefaultMaxIdleConnsPerHost = 2
    59  
    60  // Transport is an implementation of RoundTripper that supports HTTP,
    61  // HTTPS, and HTTP proxies (for either HTTP or HTTPS with CONNECT).
    62  //
    63  // By default, Transport caches connections for future re-use.
    64  // This may leave many open connections when accessing many hosts.
    65  // This behavior can be managed using Transport's CloseIdleConnections method
    66  // and the MaxIdleConnsPerHost and DisableKeepAlives fields.
    67  //
    68  // Transports should be reused instead of created as needed.
    69  // Transports are safe for concurrent use by multiple goroutines.
    70  //
    71  // A Transport is a low-level primitive for making HTTP and HTTPS requests.
    72  // For high-level functionality, such as cookies and redirects, see Client.
    73  //
    74  // Transport uses HTTP/1.1 for HTTP URLs and either HTTP/1.1 or HTTP/2
    75  // for HTTPS URLs, depending on whether the server supports HTTP/2,
    76  // and how the Transport is configured. The DefaultTransport supports HTTP/2.
    77  // To explicitly enable HTTP/2 on a transport, use golang.org/x/net/http2
    78  // and call ConfigureTransport. See the package docs for more about HTTP/2.
    79  //
    80  // Responses with status codes in the 1xx range are either handled
    81  // automatically (100 expect-continue) or ignored. The one
    82  // exception is HTTP status code 101 (Switching Protocols), which is
    83  // considered a terminal status and returned by RoundTrip. To see the
    84  // ignored 1xx responses, use the httptrace trace package's
    85  // ClientTrace.Got1xxResponse.
    86  //
    87  // Transport only retries a request upon encountering a network error
    88  // if the request is idempotent and either has no body or has its
    89  // Request.GetBody defined. HTTP requests are considered idempotent if
    90  // they have HTTP methods GET, HEAD, OPTIONS, or TRACE; or if their
    91  // Header map contains an "Idempotency-Key" or "X-Idempotency-Key"
    92  // entry. If the idempotency key value is a zero-length slice, the
    93  // request is treated as idempotent but the header is not sent on the
    94  // wire.
    95  type Transport struct {
    96  	idleMu       sync.Mutex
    97  	closeIdle    bool                                // user has requested to close all idle conns
    98  	idleConn     map[connectMethodKey][]*persistConn // most recently used at end
    99  	idleConnWait map[connectMethodKey]wantConnQueue  // waiting getConns
   100  	idleLRU      connLRU
   101  
   102  	reqMu       sync.Mutex
   103  	reqCanceler map[cancelKey]func(error)
   104  
   105  	altMu    sync.Mutex   // guards changing altProto only
   106  	altProto atomic.Value // of nil or map[string]RoundTripper, key is URI scheme
   107  
   108  	connsPerHostMu   sync.Mutex
   109  	connsPerHost     map[connectMethodKey]int
   110  	connsPerHostWait map[connectMethodKey]wantConnQueue // waiting getConns
   111  
   112  	// Proxy specifies a function to return a proxy for a given
   113  	// Request. If the function returns a non-nil error, the
   114  	// request is aborted with the provided error.
   115  	//
   116  	// The proxy type is determined by the URL scheme. "http",
   117  	// "https", and "socks5" are supported. If the scheme is empty,
   118  	// "http" is assumed.
   119  	//
   120  	// If Proxy is nil or returns a nil *URL, no proxy is used.
   121  	Proxy func(*Request) (*url.URL, error)
   122  
   123  	// DialContext specifies the dial function for creating unencrypted TCP connections.
   124  	// If DialContext is nil (and the deprecated Dial below is also nil),
   125  	// then the transport dials using package net.
   126  	//
   127  	// DialContext runs concurrently with calls to RoundTrip.
   128  	// A RoundTrip call that initiates a dial may end up using
   129  	// a connection dialed previously when the earlier connection
   130  	// becomes idle before the later DialContext completes.
   131  	DialContext func(ctx context.Context, network, addr string) (net.Conn, error)
   132  
   133  	// Dial specifies the dial function for creating unencrypted TCP connections.
   134  	//
   135  	// Dial runs concurrently with calls to RoundTrip.
   136  	// A RoundTrip call that initiates a dial may end up using
   137  	// a connection dialed previously when the earlier connection
   138  	// becomes idle before the later Dial completes.
   139  	//
   140  	// Deprecated: Use DialContext instead, which allows the transport
   141  	// to cancel dials as soon as they are no longer needed.
   142  	// If both are set, DialContext takes priority.
   143  	Dial func(network, addr string) (net.Conn, error)
   144  
   145  	// DialTLSContext specifies an optional dial function for creating
   146  	// TLS connections for non-proxied HTTPS requests.
   147  	//
   148  	// If DialTLSContext is nil (and the deprecated DialTLS below is also nil),
   149  	// DialContext and TLSClientConfig are used.
   150  	//
   151  	// If DialTLSContext is set, the Dial and DialContext hooks are not used for HTTPS
   152  	// requests and the TLSClientConfig and TLSHandshakeTimeout
   153  	// are ignored. The returned net.Conn is assumed to already be
   154  	// past the TLS handshake.
   155  	DialTLSContext func(ctx context.Context, network, addr string) (net.Conn, error)
   156  
   157  	// DialTLS specifies an optional dial function for creating
   158  	// TLS connections for non-proxied HTTPS requests.
   159  	//
   160  	// Deprecated: Use DialTLSContext instead, which allows the transport
   161  	// to cancel dials as soon as they are no longer needed.
   162  	// If both are set, DialTLSContext takes priority.
   163  	DialTLS func(network, addr string) (net.Conn, error)
   164  
   165  	// TLSClientConfig specifies the TLS configuration to use with
   166  	// tls.Client.
   167  	// If nil, the default configuration is used.
   168  	// If non-nil, HTTP/2 support may not be enabled by default.
   169  	TLSClientConfig *tls.Config
   170  
   171  	// TLSHandshakeTimeout specifies the maximum amount of time waiting to
   172  	// wait for a TLS handshake. Zero means no timeout.
   173  	TLSHandshakeTimeout time.Duration
   174  
   175  	// DisableKeepAlives, if true, disables HTTP keep-alives and
   176  	// will only use the connection to the server for a single
   177  	// HTTP request.
   178  	//
   179  	// This is unrelated to the similarly named TCP keep-alives.
   180  	DisableKeepAlives bool
   181  
   182  	// DisableCompression, if true, prevents the Transport from
   183  	// requesting compression with an "Accept-Encoding: gzip"
   184  	// request header when the Request contains no existing
   185  	// Accept-Encoding value. If the Transport requests gzip on
   186  	// its own and gets a gzipped response, it's transparently
   187  	// decoded in the Response.Body. However, if the user
   188  	// explicitly requested gzip it is not automatically
   189  	// uncompressed.
   190  	DisableCompression bool
   191  
   192  	// MaxIdleConns controls the maximum number of idle (keep-alive)
   193  	// connections across all hosts. Zero means no limit.
   194  	MaxIdleConns int
   195  
   196  	// MaxIdleConnsPerHost, if non-zero, controls the maximum idle
   197  	// (keep-alive) connections to keep per-host. If zero,
   198  	// DefaultMaxIdleConnsPerHost is used.
   199  	MaxIdleConnsPerHost int
   200  
   201  	// MaxConnsPerHost optionally limits the total number of
   202  	// connections per host, including connections in the dialing,
   203  	// active, and idle states. On limit violation, dials will block.
   204  	//
   205  	// Zero means no limit.
   206  	MaxConnsPerHost int
   207  
   208  	// IdleConnTimeout is the maximum amount of time an idle
   209  	// (keep-alive) connection will remain idle before closing
   210  	// itself.
   211  	// Zero means no limit.
   212  	IdleConnTimeout time.Duration
   213  
   214  	// ResponseHeaderTimeout, if non-zero, specifies the amount of
   215  	// time to wait for a server's response headers after fully
   216  	// writing the request (including its body, if any). This
   217  	// time does not include the time to read the response body.
   218  	ResponseHeaderTimeout time.Duration
   219  
   220  	// ExpectContinueTimeout, if non-zero, specifies the amount of
   221  	// time to wait for a server's first response headers after fully
   222  	// writing the request headers if the request has an
   223  	// "Expect: 100-continue" header. Zero means no timeout and
   224  	// causes the body to be sent immediately, without
   225  	// waiting for the server to approve.
   226  	// This time does not include the time to send the request header.
   227  	ExpectContinueTimeout time.Duration
   228  
   229  	// TLSNextProto specifies how the Transport switches to an
   230  	// alternate protocol (such as HTTP/2) after a TLS ALPN
   231  	// protocol negotiation. If Transport dials an TLS connection
   232  	// with a non-empty protocol name and TLSNextProto contains a
   233  	// map entry for that key (such as "h2"), then the func is
   234  	// called with the request's authority (such as "example.com"
   235  	// or "example.com:1234") and the TLS connection. The function
   236  	// must return a RoundTripper that then handles the request.
   237  	// If TLSNextProto is not nil, HTTP/2 support is not enabled
   238  	// automatically.
   239  	TLSNextProto map[string]func(authority string, c *tls.Conn) RoundTripper
   240  
   241  	// ProxyConnectHeader optionally specifies headers to send to
   242  	// proxies during CONNECT requests.
   243  	ProxyConnectHeader Header
   244  
   245  	// MaxResponseHeaderBytes specifies a limit on how many
   246  	// response bytes are allowed in the server's response
   247  	// header.
   248  	//
   249  	// Zero means to use a default limit.
   250  	MaxResponseHeaderBytes int64
   251  
   252  	// WriteBufferSize specifies the size of the write buffer used
   253  	// when writing to the transport.
   254  	// If zero, a default (currently 4KB) is used.
   255  	WriteBufferSize int
   256  
   257  	// ReadBufferSize specifies the size of the read buffer used
   258  	// when reading from the transport.
   259  	// If zero, a default (currently 4KB) is used.
   260  	ReadBufferSize int
   261  
   262  	// nextProtoOnce guards initialization of TLSNextProto and
   263  	// h2transport (via onceSetNextProtoDefaults)
   264  	nextProtoOnce      sync.Once
   265  	h2transport        h2Transport // non-nil if http2 wired up
   266  	tlsNextProtoWasNil bool        // whether TLSNextProto was nil when the Once fired
   267  
   268  	// ForceAttemptHTTP2 controls whether HTTP/2 is enabled when a non-zero
   269  	// Dial, DialTLS, or DialContext func or TLSClientConfig is provided.
   270  	// By default, use of any those fields conservatively disables HTTP/2.
   271  	// To use a custom dialer or TLS config and still attempt HTTP/2
   272  	// upgrades, set this to true.
   273  	ForceAttemptHTTP2 bool
   274  }
   275  
   276  // A cancelKey is the key of the reqCanceler map.
   277  // We wrap the *Request in this type since we want to use the original request,
   278  // not any transient one created by roundTrip.
   279  type cancelKey struct {
   280  	req *Request
   281  }
   282  
   283  func (t *Transport) writeBufferSize() int {
   284  	if t.WriteBufferSize > 0 {
   285  		return t.WriteBufferSize
   286  	}
   287  	return 4 << 10
   288  }
   289  
   290  func (t *Transport) readBufferSize() int {
   291  	if t.ReadBufferSize > 0 {
   292  		return t.ReadBufferSize
   293  	}
   294  	return 4 << 10
   295  }
   296  
   297  // Clone returns a deep copy of t's exported fields.
   298  func (t *Transport) Clone() *Transport {
   299  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   300  	t2 := &Transport{
   301  		Proxy:                  t.Proxy,
   302  		DialContext:            t.DialContext,
   303  		Dial:                   t.Dial,
   304  		DialTLS:                t.DialTLS,
   305  		DialTLSContext:         t.DialTLSContext,
   306  		TLSHandshakeTimeout:    t.TLSHandshakeTimeout,
   307  		DisableKeepAlives:      t.DisableKeepAlives,
   308  		DisableCompression:     t.DisableCompression,
   309  		MaxIdleConns:           t.MaxIdleConns,
   310  		MaxIdleConnsPerHost:    t.MaxIdleConnsPerHost,
   311  		MaxConnsPerHost:        t.MaxConnsPerHost,
   312  		IdleConnTimeout:        t.IdleConnTimeout,
   313  		ResponseHeaderTimeout:  t.ResponseHeaderTimeout,
   314  		ExpectContinueTimeout:  t.ExpectContinueTimeout,
   315  		ProxyConnectHeader:     t.ProxyConnectHeader.Clone(),
   316  		MaxResponseHeaderBytes: t.MaxResponseHeaderBytes,
   317  		ForceAttemptHTTP2:      t.ForceAttemptHTTP2,
   318  		WriteBufferSize:        t.WriteBufferSize,
   319  		ReadBufferSize:         t.ReadBufferSize,
   320  	}
   321  	if t.TLSClientConfig != nil {
   322  		t2.TLSClientConfig = t.TLSClientConfig.Clone()
   323  	}
   324  	if !t.tlsNextProtoWasNil {
   325  		npm := map[string]func(authority string, c *tls.Conn) RoundTripper{}
   326  		for k, v := range t.TLSNextProto {
   327  			npm[k] = v
   328  		}
   329  		t2.TLSNextProto = npm
   330  	}
   331  	return t2
   332  }
   333  
   334  // h2Transport is the interface we expect to be able to call from
   335  // net/http against an *http2.Transport that's either bundled into
   336  // h2_bundle.go or supplied by the user via x/net/http2.
   337  //
   338  // We name it with the "h2" prefix to stay out of the "http2" prefix
   339  // namespace used by x/tools/cmd/bundle for h2_bundle.go.
   340  type h2Transport interface {
   341  	CloseIdleConnections()
   342  }
   343  
   344  func (t *Transport) hasCustomTLSDialer() bool {
   345  	return t.DialTLS != nil || t.DialTLSContext != nil
   346  }
   347  
   348  // onceSetNextProtoDefaults initializes TLSNextProto.
   349  // It must be called via t.nextProtoOnce.Do.
   350  func (t *Transport) onceSetNextProtoDefaults() {
   351  	t.tlsNextProtoWasNil = (t.TLSNextProto == nil)
   352  	if strings.Contains(os.Getenv("GODEBUG"), "http2client=0") {
   353  		return
   354  	}
   355  
   356  	// If they've already configured http2 with
   357  	// golang.org/x/net/http2 instead of the bundled copy, try to
   358  	// get at its http2.Transport value (via the "https"
   359  	// altproto map) so we can call CloseIdleConnections on it if
   360  	// requested. (Issue 22891)
   361  	altProto, _ := t.altProto.Load().(map[string]RoundTripper)
   362  	if rv := reflect.ValueOf(altProto["https"]); rv.IsValid() && rv.Type().Kind() == reflect.Struct && rv.Type().NumField() == 1 {
   363  		if v := rv.Field(0); v.CanInterface() {
   364  			if h2i, ok := v.Interface().(h2Transport); ok {
   365  				t.h2transport = h2i
   366  				return
   367  			}
   368  		}
   369  	}
   370  
   371  	if t.TLSNextProto != nil {
   372  		// This is the documented way to disable http2 on a
   373  		// Transport.
   374  		return
   375  	}
   376  	if !t.ForceAttemptHTTP2 && (t.TLSClientConfig != nil || t.Dial != nil || t.DialContext != nil || t.hasCustomTLSDialer()) {
   377  		// Be conservative and don't automatically enable
   378  		// http2 if they've specified a custom TLS config or
   379  		// custom dialers. Let them opt-in themselves via
   380  		// http2.ConfigureTransport so we don't surprise them
   381  		// by modifying their tls.Config. Issue 14275.
   382  		// However, if ForceAttemptHTTP2 is true, it overrides the above checks.
   383  		return
   384  	}
   385  	if omitBundledHTTP2 {
   386  		return
   387  	}
   388  	t2, err := http2configureTransport(t)
   389  	if err != nil {
   390  		log.Printf("Error enabling Transport HTTP/2 support: %v", err)
   391  		return
   392  	}
   393  	t.h2transport = t2
   394  
   395  	// Auto-configure the http2.Transport's MaxHeaderListSize from
   396  	// the http.Transport's MaxResponseHeaderBytes. They don't
   397  	// exactly mean the same thing, but they're close.
   398  	//
   399  	// TODO: also add this to x/net/http2.Configure Transport, behind
   400  	// a +build go1.7 build tag:
   401  	if limit1 := t.MaxResponseHeaderBytes; limit1 != 0 && t2.MaxHeaderListSize == 0 {
   402  		const h2max = 1<<32 - 1
   403  		if limit1 >= h2max {
   404  			t2.MaxHeaderListSize = h2max
   405  		} else {
   406  			t2.MaxHeaderListSize = uint32(limit1)
   407  		}
   408  	}
   409  }
   410  
   411  // ProxyFromEnvironment returns the URL of the proxy to use for a
   412  // given request, as indicated by the environment variables
   413  // HTTP_PROXY, HTTPS_PROXY and NO_PROXY (or the lowercase versions
   414  // thereof). HTTPS_PROXY takes precedence over HTTP_PROXY for https
   415  // requests.
   416  //
   417  // The environment values may be either a complete URL or a
   418  // "host[:port]", in which case the "http" scheme is assumed.
   419  // An error is returned if the value is a different form.
   420  //
   421  // A nil URL and nil error are returned if no proxy is defined in the
   422  // environment, or a proxy should not be used for the given request,
   423  // as defined by NO_PROXY.
   424  //
   425  // As a special case, if req.URL.Host is "localhost" (with or without
   426  // a port number), then a nil URL and nil error will be returned.
   427  func ProxyFromEnvironment(req *Request) (*url.URL, error) {
   428  	return envProxyFunc()(req.URL)
   429  }
   430  
   431  // ProxyURL returns a proxy function (for use in a Transport)
   432  // that always returns the same URL.
   433  func ProxyURL(fixedURL *url.URL) func(*Request) (*url.URL, error) {
   434  	return func(*Request) (*url.URL, error) {
   435  		return fixedURL, nil
   436  	}
   437  }
   438  
   439  // transportRequest is a wrapper around a *Request that adds
   440  // optional extra headers to write and stores any error to return
   441  // from roundTrip.
   442  type transportRequest struct {
   443  	*Request                         // original request, not to be mutated
   444  	extra     Header                 // extra headers to write, or nil
   445  	trace     *httptrace.ClientTrace // optional
   446  	cancelKey cancelKey
   447  
   448  	mu  sync.Mutex // guards err
   449  	err error      // first setError value for mapRoundTripError to consider
   450  }
   451  
   452  func (tr *transportRequest) extraHeaders() Header {
   453  	if tr.extra == nil {
   454  		tr.extra = make(Header)
   455  	}
   456  	return tr.extra
   457  }
   458  
   459  func (tr *transportRequest) setError(err error) {
   460  	tr.mu.Lock()
   461  	if tr.err == nil {
   462  		tr.err = err
   463  	}
   464  	tr.mu.Unlock()
   465  }
   466  
   467  // useRegisteredProtocol reports whether an alternate protocol (as registered
   468  // with Transport.RegisterProtocol) should be respected for this request.
   469  func (t *Transport) useRegisteredProtocol(req *Request) bool {
   470  	if req.URL.Scheme == "https" && req.requiresHTTP1() {
   471  		// If this request requires HTTP/1, don't use the
   472  		// "https" alternate protocol, which is used by the
   473  		// HTTP/2 code to take over requests if there's an
   474  		// existing cached HTTP/2 connection.
   475  		return false
   476  	}
   477  	return true
   478  }
   479  
   480  // alternateRoundTripper returns the alternate RoundTripper to use
   481  // for this request if the Request's URL scheme requires one,
   482  // or nil for the normal case of using the Transport.
   483  func (t *Transport) alternateRoundTripper(req *Request) RoundTripper {
   484  	if !t.useRegisteredProtocol(req) {
   485  		return nil
   486  	}
   487  	altProto, _ := t.altProto.Load().(map[string]RoundTripper)
   488  	return altProto[req.URL.Scheme]
   489  }
   490  
   491  // roundTrip implements a RoundTripper over HTTP.
   492  func (t *Transport) roundTrip(req *Request) (*Response, error) {
   493  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   494  	ctx := req.Context()
   495  	trace := httptrace.ContextClientTrace(ctx)
   496  
   497  	if req.URL == nil {
   498  		req.closeBody()
   499  		return nil, errors.New("http: nil Request.URL")
   500  	}
   501  	if req.Header == nil {
   502  		req.closeBody()
   503  		return nil, errors.New("http: nil Request.Header")
   504  	}
   505  	scheme := req.URL.Scheme
   506  	isHTTP := scheme == "http" || scheme == "https"
   507  	if isHTTP {
   508  		for k, vv := range req.Header {
   509  			if !httpguts.ValidHeaderFieldName(k) {
   510  				req.closeBody()
   511  				return nil, fmt.Errorf("net/http: invalid header field name %q", k)
   512  			}
   513  			for _, v := range vv {
   514  				if !httpguts.ValidHeaderFieldValue(v) {
   515  					req.closeBody()
   516  					return nil, fmt.Errorf("net/http: invalid header field value %q for key %v", v, k)
   517  				}
   518  			}
   519  		}
   520  	}
   521  
   522  	origReq := req
   523  	cancelKey := cancelKey{origReq}
   524  	req = setupRewindBody(req)
   525  
   526  	if altRT := t.alternateRoundTripper(req); altRT != nil {
   527  		if resp, err := altRT.RoundTrip(req); err != ErrSkipAltProtocol {
   528  			return resp, err
   529  		}
   530  		var err error
   531  		req, err = rewindBody(req)
   532  		if err != nil {
   533  			return nil, err
   534  		}
   535  	}
   536  	if !isHTTP {
   537  		req.closeBody()
   538  		return nil, badStringError("unsupported protocol scheme", scheme)
   539  	}
   540  	if req.Method != "" && !validMethod(req.Method) {
   541  		req.closeBody()
   542  		return nil, fmt.Errorf("net/http: invalid method %q", req.Method)
   543  	}
   544  	if req.URL.Host == "" {
   545  		req.closeBody()
   546  		return nil, errors.New("http: no Host in request URL")
   547  	}
   548  
   549  	for {
   550  		select {
   551  		case <-ctx.Done():
   552  			req.closeBody()
   553  			return nil, ctx.Err()
   554  		default:
   555  		}
   556  
   557  		// treq gets modified by roundTrip, so we need to recreate for each retry.
   558  		treq := &transportRequest{Request: req, trace: trace, cancelKey: cancelKey}
   559  		cm, err := t.connectMethodForRequest(treq)
   560  		if err != nil {
   561  			req.closeBody()
   562  			return nil, err
   563  		}
   564  
   565  		// Get the cached or newly-created connection to either the
   566  		// host (for http or https), the http proxy, or the http proxy
   567  		// pre-CONNECTed to https server. In any case, we'll be ready
   568  		// to send it requests.
   569  		pconn, err := t.getConn(treq, cm)
   570  		if err != nil {
   571  			t.setReqCanceler(cancelKey, nil)
   572  			req.closeBody()
   573  			return nil, err
   574  		}
   575  
   576  		var resp *Response
   577  		if pconn.alt != nil {
   578  			// HTTP/2 path.
   579  			t.setReqCanceler(cancelKey, nil) // not cancelable with CancelRequest
   580  			resp, err = pconn.alt.RoundTrip(req)
   581  		} else {
   582  			resp, err = pconn.roundTrip(treq)
   583  		}
   584  		if err == nil {
   585  			resp.Request = origReq
   586  			return resp, nil
   587  		}
   588  
   589  		// Failed. Clean up and determine whether to retry.
   590  		if http2isNoCachedConnError(err) {
   591  			if t.removeIdleConn(pconn) {
   592  				t.decConnsPerHost(pconn.cacheKey)
   593  			}
   594  		} else if !pconn.shouldRetryRequest(req, err) {
   595  			// Issue 16465: return underlying net.Conn.Read error from peek,
   596  			// as we've historically done.
   597  			if e, ok := err.(transportReadFromServerError); ok {
   598  				err = e.err
   599  			}
   600  			return nil, err
   601  		}
   602  		testHookRoundTripRetried()
   603  
   604  		// Rewind the body if we're able to.
   605  		req, err = rewindBody(req)
   606  		if err != nil {
   607  			return nil, err
   608  		}
   609  	}
   610  }
   611  
   612  var errCannotRewind = errors.New("net/http: cannot rewind body after connection loss")
   613  
   614  type readTrackingBody struct {
   615  	io.ReadCloser
   616  	didRead bool
   617  }
   618  
   619  func (r *readTrackingBody) Read(data []byte) (int, error) {
   620  	r.didRead = true
   621  	return r.ReadCloser.Read(data)
   622  }
   623  
   624  // setupRewindBody returns a new request with a custom body wrapper
   625  // that can report whether the body needs rewinding.
   626  // This lets rewindBody avoid an error result when the request
   627  // does not have GetBody but the body hasn't been read at all yet.
   628  func setupRewindBody(req *Request) *Request {
   629  	if req.Body == nil || req.Body == NoBody {
   630  		return req
   631  	}
   632  	newReq := *req
   633  	newReq.Body = &readTrackingBody{ReadCloser: req.Body}
   634  	return &newReq
   635  }
   636  
   637  // rewindBody returns a new request with the body rewound.
   638  // It returns req unmodified if the body does not need rewinding.
   639  // rewindBody takes care of closing req.Body when appropriate
   640  // (in all cases except when rewindBody returns req unmodified).
   641  func rewindBody(req *Request) (rewound *Request, err error) {
   642  	if req.Body == nil || req.Body == NoBody || !req.Body.(*readTrackingBody).didRead {
   643  		return req, nil // nothing to rewind
   644  	}
   645  	req.closeBody()
   646  	if req.GetBody == nil {
   647  		return nil, errCannotRewind
   648  	}
   649  	body, err := req.GetBody()
   650  	if err != nil {
   651  		return nil, err
   652  	}
   653  	newReq := *req
   654  	newReq.Body = &readTrackingBody{ReadCloser: body}
   655  	return &newReq, nil
   656  }
   657  
   658  // shouldRetryRequest reports whether we should retry sending a failed
   659  // HTTP request on a new connection. The non-nil input error is the
   660  // error from roundTrip.
   661  func (pc *persistConn) shouldRetryRequest(req *Request, err error) bool {
   662  	if http2isNoCachedConnError(err) {
   663  		// Issue 16582: if the user started a bunch of
   664  		// requests at once, they can all pick the same conn
   665  		// and violate the server's max concurrent streams.
   666  		// Instead, match the HTTP/1 behavior for now and dial
   667  		// again to get a new TCP connection, rather than failing
   668  		// this request.
   669  		return true
   670  	}
   671  	if err == errMissingHost {
   672  		// User error.
   673  		return false
   674  	}
   675  	if !pc.isReused() {
   676  		// This was a fresh connection. There's no reason the server
   677  		// should've hung up on us.
   678  		//
   679  		// Also, if we retried now, we could loop forever
   680  		// creating new connections and retrying if the server
   681  		// is just hanging up on us because it doesn't like
   682  		// our request (as opposed to sending an error).
   683  		return false
   684  	}
   685  	if _, ok := err.(nothingWrittenError); ok {
   686  		// We never wrote anything, so it's safe to retry, if there's no body or we
   687  		// can "rewind" the body with GetBody.
   688  		return req.outgoingLength() == 0 || req.GetBody != nil
   689  	}
   690  	if !req.isReplayable() {
   691  		// Don't retry non-idempotent requests.
   692  		return false
   693  	}
   694  	if _, ok := err.(transportReadFromServerError); ok {
   695  		// We got some non-EOF net.Conn.Read failure reading
   696  		// the 1st response byte from the server.
   697  		return true
   698  	}
   699  	if err == errServerClosedIdle {
   700  		// The server replied with io.EOF while we were trying to
   701  		// read the response. Probably an unfortunately keep-alive
   702  		// timeout, just as the client was writing a request.
   703  		return true
   704  	}
   705  	return false // conservatively
   706  }
   707  
   708  // ErrSkipAltProtocol is a sentinel error value defined by Transport.RegisterProtocol.
   709  var ErrSkipAltProtocol = errors.New("net/http: skip alternate protocol")
   710  
   711  // RegisterProtocol registers a new protocol with scheme.
   712  // The Transport will pass requests using the given scheme to rt.
   713  // It is rt's responsibility to simulate HTTP request semantics.
   714  //
   715  // RegisterProtocol can be used by other packages to provide
   716  // implementations of protocol schemes like "ftp" or "file".
   717  //
   718  // If rt.RoundTrip returns ErrSkipAltProtocol, the Transport will
   719  // handle the RoundTrip itself for that one request, as if the
   720  // protocol were not registered.
   721  func (t *Transport) RegisterProtocol(scheme string, rt RoundTripper) {
   722  	t.altMu.Lock()
   723  	defer t.altMu.Unlock()
   724  	oldMap, _ := t.altProto.Load().(map[string]RoundTripper)
   725  	if _, exists := oldMap[scheme]; exists {
   726  		panic("protocol " + scheme + " already registered")
   727  	}
   728  	newMap := make(map[string]RoundTripper)
   729  	for k, v := range oldMap {
   730  		newMap[k] = v
   731  	}
   732  	newMap[scheme] = rt
   733  	t.altProto.Store(newMap)
   734  }
   735  
   736  // CloseIdleConnections closes any connections which were previously
   737  // connected from previous requests but are now sitting idle in
   738  // a "keep-alive" state. It does not interrupt any connections currently
   739  // in use.
   740  func (t *Transport) CloseIdleConnections() {
   741  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   742  	t.idleMu.Lock()
   743  	m := t.idleConn
   744  	t.idleConn = nil
   745  	t.closeIdle = true // close newly idle connections
   746  	t.idleLRU = connLRU{}
   747  	t.idleMu.Unlock()
   748  	for _, conns := range m {
   749  		for _, pconn := range conns {
   750  			pconn.close(errCloseIdleConns)
   751  		}
   752  	}
   753  	if t2 := t.h2transport; t2 != nil {
   754  		t2.CloseIdleConnections()
   755  	}
   756  }
   757  
   758  // CancelRequest cancels an in-flight request by closing its connection.
   759  // CancelRequest should only be called after RoundTrip has returned.
   760  //
   761  // Deprecated: Use Request.WithContext to create a request with a
   762  // cancelable context instead. CancelRequest cannot cancel HTTP/2
   763  // requests.
   764  func (t *Transport) CancelRequest(req *Request) {
   765  	t.cancelRequest(cancelKey{req}, errRequestCanceled)
   766  }
   767  
   768  // Cancel an in-flight request, recording the error value.
   769  func (t *Transport) cancelRequest(key cancelKey, err error) {
   770  	t.reqMu.Lock()
   771  	cancel := t.reqCanceler[key]
   772  	delete(t.reqCanceler, key)
   773  	t.reqMu.Unlock()
   774  	if cancel != nil {
   775  		cancel(err)
   776  	}
   777  }
   778  
   779  //
   780  // Private implementation past this point.
   781  //
   782  
   783  var (
   784  	// proxyConfigOnce guards proxyConfig
   785  	envProxyOnce      sync.Once
   786  	envProxyFuncValue func(*url.URL) (*url.URL, error)
   787  )
   788  
   789  // defaultProxyConfig returns a ProxyConfig value looked up
   790  // from the environment. This mitigates expensive lookups
   791  // on some platforms (e.g. Windows).
   792  func envProxyFunc() func(*url.URL) (*url.URL, error) {
   793  	envProxyOnce.Do(func() {
   794  		envProxyFuncValue = httpproxy.FromEnvironment().ProxyFunc()
   795  	})
   796  	return envProxyFuncValue
   797  }
   798  
   799  // resetProxyConfig is used by tests.
   800  func resetProxyConfig() {
   801  	envProxyOnce = sync.Once{}
   802  	envProxyFuncValue = nil
   803  }
   804  
   805  func (t *Transport) connectMethodForRequest(treq *transportRequest) (cm connectMethod, err error) {
   806  	cm.targetScheme = treq.URL.Scheme
   807  	cm.targetAddr = canonicalAddr(treq.URL)
   808  	if t.Proxy != nil {
   809  		cm.proxyURL, err = t.Proxy(treq.Request)
   810  	}
   811  	cm.onlyH1 = treq.requiresHTTP1()
   812  	return cm, err
   813  }
   814  
   815  // proxyAuth returns the Proxy-Authorization header to set
   816  // on requests, if applicable.
   817  func (cm *connectMethod) proxyAuth() string {
   818  	if cm.proxyURL == nil {
   819  		return ""
   820  	}
   821  	if u := cm.proxyURL.User; u != nil {
   822  		username := u.Username()
   823  		password, _ := u.Password()
   824  		return "Basic " + basicAuth(username, password)
   825  	}
   826  	return ""
   827  }
   828  
   829  // error values for debugging and testing, not seen by users.
   830  var (
   831  	errKeepAlivesDisabled = errors.New("http: putIdleConn: keep alives disabled")
   832  	errConnBroken         = errors.New("http: putIdleConn: connection is in bad state")
   833  	errCloseIdle          = errors.New("http: putIdleConn: CloseIdleConnections was called")
   834  	errTooManyIdle        = errors.New("http: putIdleConn: too many idle connections")
   835  	errTooManyIdleHost    = errors.New("http: putIdleConn: too many idle connections for host")
   836  	errCloseIdleConns     = errors.New("http: CloseIdleConnections called")
   837  	errReadLoopExiting    = errors.New("http: persistConn.readLoop exiting")
   838  	errIdleConnTimeout    = errors.New("http: idle connection timeout")
   839  
   840  	// errServerClosedIdle is not seen by users for idempotent requests, but may be
   841  	// seen by a user if the server shuts down an idle connection and sends its FIN
   842  	// in flight with already-written POST body bytes from the client.
   843  	// See https://github.com/golang/go/issues/19943#issuecomment-355607646
   844  	errServerClosedIdle = errors.New("http: server closed idle connection")
   845  )
   846  
   847  // transportReadFromServerError is used by Transport.readLoop when the
   848  // 1 byte peek read fails and we're actually anticipating a response.
   849  // Usually this is just due to the inherent keep-alive shut down race,
   850  // where the server closed the connection at the same time the client
   851  // wrote. The underlying err field is usually io.EOF or some
   852  // ECONNRESET sort of thing which varies by platform. But it might be
   853  // the user's custom net.Conn.Read error too, so we carry it along for
   854  // them to return from Transport.RoundTrip.
   855  type transportReadFromServerError struct {
   856  	err error
   857  }
   858  
   859  func (e transportReadFromServerError) Unwrap() error { return e.err }
   860  
   861  func (e transportReadFromServerError) Error() string {
   862  	return fmt.Sprintf("net/http: Transport failed to read from server: %v", e.err)
   863  }
   864  
   865  func (t *Transport) putOrCloseIdleConn(pconn *persistConn) {
   866  	if err := t.tryPutIdleConn(pconn); err != nil {
   867  		pconn.close(err)
   868  	}
   869  }
   870  
   871  func (t *Transport) maxIdleConnsPerHost() int {
   872  	if v := t.MaxIdleConnsPerHost; v != 0 {
   873  		return v
   874  	}
   875  	return DefaultMaxIdleConnsPerHost
   876  }
   877  
   878  // tryPutIdleConn adds pconn to the list of idle persistent connections awaiting
   879  // a new request.
   880  // If pconn is no longer needed or not in a good state, tryPutIdleConn returns
   881  // an error explaining why it wasn't registered.
   882  // tryPutIdleConn does not close pconn. Use putOrCloseIdleConn instead for that.
   883  func (t *Transport) tryPutIdleConn(pconn *persistConn) error {
   884  	if t.DisableKeepAlives || t.MaxIdleConnsPerHost < 0 {
   885  		return errKeepAlivesDisabled
   886  	}
   887  	if pconn.isBroken() {
   888  		return errConnBroken
   889  	}
   890  	pconn.markReused()
   891  
   892  	t.idleMu.Lock()
   893  	defer t.idleMu.Unlock()
   894  
   895  	// HTTP/2 (pconn.alt != nil) connections do not come out of the idle list,
   896  	// because multiple goroutines can use them simultaneously.
   897  	// If this is an HTTP/2 connection being “returned,” we're done.
   898  	if pconn.alt != nil && t.idleLRU.m[pconn] != nil {
   899  		return nil
   900  	}
   901  
   902  	// Deliver pconn to goroutine waiting for idle connection, if any.
   903  	// (They may be actively dialing, but this conn is ready first.
   904  	// Chrome calls this socket late binding.
   905  	// See https://www.chromium.org/developers/design-documents/network-stack#TOC-Connection-Management.)
   906  	key := pconn.cacheKey
   907  	if q, ok := t.idleConnWait[key]; ok {
   908  		done := false
   909  		if pconn.alt == nil {
   910  			// HTTP/1.
   911  			// Loop over the waiting list until we find a w that isn't done already, and hand it pconn.
   912  			for q.len() > 0 {
   913  				w := q.popFront()
   914  				if w.tryDeliver(pconn, nil) {
   915  					done = true
   916  					break
   917  				}
   918  			}
   919  		} else {
   920  			// HTTP/2.
   921  			// Can hand the same pconn to everyone in the waiting list,
   922  			// and we still won't be done: we want to put it in the idle
   923  			// list unconditionally, for any future clients too.
   924  			for q.len() > 0 {
   925  				w := q.popFront()
   926  				w.tryDeliver(pconn, nil)
   927  			}
   928  		}
   929  		if q.len() == 0 {
   930  			delete(t.idleConnWait, key)
   931  		} else {
   932  			t.idleConnWait[key] = q
   933  		}
   934  		if done {
   935  			return nil
   936  		}
   937  	}
   938  
   939  	if t.closeIdle {
   940  		return errCloseIdle
   941  	}
   942  	if t.idleConn == nil {
   943  		t.idleConn = make(map[connectMethodKey][]*persistConn)
   944  	}
   945  	idles := t.idleConn[key]
   946  	if len(idles) >= t.maxIdleConnsPerHost() {
   947  		return errTooManyIdleHost
   948  	}
   949  	for _, exist := range idles {
   950  		if exist == pconn {
   951  			log.Fatalf("dup idle pconn %p in freelist", pconn)
   952  		}
   953  	}
   954  	t.idleConn[key] = append(idles, pconn)
   955  	t.idleLRU.add(pconn)
   956  	if t.MaxIdleConns != 0 && t.idleLRU.len() > t.MaxIdleConns {
   957  		oldest := t.idleLRU.removeOldest()
   958  		oldest.close(errTooManyIdle)
   959  		t.removeIdleConnLocked(oldest)
   960  	}
   961  
   962  	// Set idle timer, but only for HTTP/1 (pconn.alt == nil).
   963  	// The HTTP/2 implementation manages the idle timer itself
   964  	// (see idleConnTimeout in h2_bundle.go).
   965  	if t.IdleConnTimeout > 0 && pconn.alt == nil {
   966  		if pconn.idleTimer != nil {
   967  			pconn.idleTimer.Reset(t.IdleConnTimeout)
   968  		} else {
   969  			pconn.idleTimer = time.AfterFunc(t.IdleConnTimeout, pconn.closeConnIfStillIdle)
   970  		}
   971  	}
   972  	pconn.idleAt = time.Now()
   973  	return nil
   974  }
   975  
   976  // queueForIdleConn queues w to receive the next idle connection for w.cm.
   977  // As an optimization hint to the caller, queueForIdleConn reports whether
   978  // it successfully delivered an already-idle connection.
   979  func (t *Transport) queueForIdleConn(w *wantConn) (delivered bool) {
   980  	if t.DisableKeepAlives {
   981  		return false
   982  	}
   983  
   984  	t.idleMu.Lock()
   985  	defer t.idleMu.Unlock()
   986  
   987  	// Stop closing connections that become idle - we might want one.
   988  	// (That is, undo the effect of t.CloseIdleConnections.)
   989  	t.closeIdle = false
   990  
   991  	if w == nil {
   992  		// Happens in test hook.
   993  		return false
   994  	}
   995  
   996  	// If IdleConnTimeout is set, calculate the oldest
   997  	// persistConn.idleAt time we're willing to use a cached idle
   998  	// conn.
   999  	var oldTime time.Time
  1000  	if t.IdleConnTimeout > 0 {
  1001  		oldTime = time.Now().Add(-t.IdleConnTimeout)
  1002  	}
  1003  
  1004  	// Look for most recently-used idle connection.
  1005  	if list, ok := t.idleConn[w.key]; ok {
  1006  		stop := false
  1007  		delivered := false
  1008  		for len(list) > 0 && !stop {
  1009  			pconn := list[len(list)-1]
  1010  
  1011  			// See whether this connection has been idle too long, considering
  1012  			// only the wall time (the Round(0)), in case this is a laptop or VM
  1013  			// coming out of suspend with previously cached idle connections.
  1014  			tooOld := !oldTime.IsZero() && pconn.idleAt.Round(0).Before(oldTime)
  1015  			if tooOld {
  1016  				// Async cleanup. Launch in its own goroutine (as if a
  1017  				// time.AfterFunc called it); it acquires idleMu, which we're
  1018  				// holding, and does a synchronous net.Conn.Close.
  1019  				go pconn.closeConnIfStillIdle()
  1020  			}
  1021  			if pconn.isBroken() || tooOld {
  1022  				// If either persistConn.readLoop has marked the connection
  1023  				// broken, but Transport.removeIdleConn has not yet removed it
  1024  				// from the idle list, or if this persistConn is too old (it was
  1025  				// idle too long), then ignore it and look for another. In both
  1026  				// cases it's already in the process of being closed.
  1027  				list = list[:len(list)-1]
  1028  				continue
  1029  			}
  1030  			delivered = w.tryDeliver(pconn, nil)
  1031  			if delivered {
  1032  				if pconn.alt != nil {
  1033  					// HTTP/2: multiple clients can share pconn.
  1034  					// Leave it in the list.
  1035  				} else {
  1036  					// HTTP/1: only one client can use pconn.
  1037  					// Remove it from the list.
  1038  					t.idleLRU.remove(pconn)
  1039  					list = list[:len(list)-1]
  1040  				}
  1041  			}
  1042  			stop = true
  1043  		}
  1044  		if len(list) > 0 {
  1045  			t.idleConn[w.key] = list
  1046  		} else {
  1047  			delete(t.idleConn, w.key)
  1048  		}
  1049  		if stop {
  1050  			return delivered
  1051  		}
  1052  	}
  1053  
  1054  	// Register to receive next connection that becomes idle.
  1055  	if t.idleConnWait == nil {
  1056  		t.idleConnWait = make(map[connectMethodKey]wantConnQueue)
  1057  	}
  1058  	q := t.idleConnWait[w.key]
  1059  	q.cleanFront()
  1060  	q.pushBack(w)
  1061  	t.idleConnWait[w.key] = q
  1062  	return false
  1063  }
  1064  
  1065  // removeIdleConn marks pconn as dead.
  1066  func (t *Transport) removeIdleConn(pconn *persistConn) bool {
  1067  	t.idleMu.Lock()
  1068  	defer t.idleMu.Unlock()
  1069  	return t.removeIdleConnLocked(pconn)
  1070  }
  1071  
  1072  // t.idleMu must be held.
  1073  func (t *Transport) removeIdleConnLocked(pconn *persistConn) bool {
  1074  	if pconn.idleTimer != nil {
  1075  		pconn.idleTimer.Stop()
  1076  	}
  1077  	t.idleLRU.remove(pconn)
  1078  	key := pconn.cacheKey
  1079  	pconns := t.idleConn[key]
  1080  	var removed bool
  1081  	switch len(pconns) {
  1082  	case 0:
  1083  		// Nothing
  1084  	case 1:
  1085  		if pconns[0] == pconn {
  1086  			delete(t.idleConn, key)
  1087  			removed = true
  1088  		}
  1089  	default:
  1090  		for i, v := range pconns {
  1091  			if v != pconn {
  1092  				continue
  1093  			}
  1094  			// Slide down, keeping most recently-used
  1095  			// conns at the end.
  1096  			copy(pconns[i:], pconns[i+1:])
  1097  			t.idleConn[key] = pconns[:len(pconns)-1]
  1098  			removed = true
  1099  			break
  1100  		}
  1101  	}
  1102  	return removed
  1103  }
  1104  
  1105  func (t *Transport) setReqCanceler(key cancelKey, fn func(error)) {
  1106  	t.reqMu.Lock()
  1107  	defer t.reqMu.Unlock()
  1108  	if t.reqCanceler == nil {
  1109  		t.reqCanceler = make(map[cancelKey]func(error))
  1110  	}
  1111  	if fn != nil {
  1112  		t.reqCanceler[key] = fn
  1113  	} else {
  1114  		delete(t.reqCanceler, key)
  1115  	}
  1116  }
  1117  
  1118  // replaceReqCanceler replaces an existing cancel function. If there is no cancel function
  1119  // for the request, we don't set the function and return false.
  1120  // Since CancelRequest will clear the canceler, we can use the return value to detect if
  1121  // the request was canceled since the last setReqCancel call.
  1122  func (t *Transport) replaceReqCanceler(key cancelKey, fn func(error)) bool {
  1123  	t.reqMu.Lock()
  1124  	defer t.reqMu.Unlock()
  1125  	_, ok := t.reqCanceler[key]
  1126  	if !ok {
  1127  		return false
  1128  	}
  1129  	if fn != nil {
  1130  		t.reqCanceler[key] = fn
  1131  	} else {
  1132  		delete(t.reqCanceler, key)
  1133  	}
  1134  	return true
  1135  }
  1136  
  1137  var zeroDialer net.Dialer
  1138  
  1139  func (t *Transport) dial(ctx context.Context, network, addr string) (net.Conn, error) {
  1140  	if t.DialContext != nil {
  1141  		return t.DialContext(ctx, network, addr)
  1142  	}
  1143  	if t.Dial != nil {
  1144  		c, err := t.Dial(network, addr)
  1145  		if c == nil && err == nil {
  1146  			err = errors.New("net/http: Transport.Dial hook returned (nil, nil)")
  1147  		}
  1148  		return c, err
  1149  	}
  1150  	return zeroDialer.DialContext(ctx, network, addr)
  1151  }
  1152  
  1153  // A wantConn records state about a wanted connection
  1154  // (that is, an active call to getConn).
  1155  // The conn may be gotten by dialing or by finding an idle connection,
  1156  // or a cancellation may make the conn no longer wanted.
  1157  // These three options are racing against each other and use
  1158  // wantConn to coordinate and agree about the winning outcome.
  1159  type wantConn struct {
  1160  	cm    connectMethod
  1161  	key   connectMethodKey // cm.key()
  1162  	ctx   context.Context  // context for dial
  1163  	ready chan struct{}    // closed when pc, err pair is delivered
  1164  
  1165  	// hooks for testing to know when dials are done
  1166  	// beforeDial is called in the getConn goroutine when the dial is queued.
  1167  	// afterDial is called when the dial is completed or cancelled.
  1168  	beforeDial func()
  1169  	afterDial  func()
  1170  
  1171  	mu  sync.Mutex // protects pc, err, close(ready)
  1172  	pc  *persistConn
  1173  	err error
  1174  }
  1175  
  1176  // waiting reports whether w is still waiting for an answer (connection or error).
  1177  func (w *wantConn) waiting() bool {
  1178  	select {
  1179  	case <-w.ready:
  1180  		return false
  1181  	default:
  1182  		return true
  1183  	}
  1184  }
  1185  
  1186  // tryDeliver attempts to deliver pc, err to w and reports whether it succeeded.
  1187  func (w *wantConn) tryDeliver(pc *persistConn, err error) bool {
  1188  	w.mu.Lock()
  1189  	defer w.mu.Unlock()
  1190  
  1191  	if w.pc != nil || w.err != nil {
  1192  		return false
  1193  	}
  1194  
  1195  	w.pc = pc
  1196  	w.err = err
  1197  	if w.pc == nil && w.err == nil {
  1198  		panic("net/http: internal error: misuse of tryDeliver")
  1199  	}
  1200  	close(w.ready)
  1201  	return true
  1202  }
  1203  
  1204  // cancel marks w as no longer wanting a result (for example, due to cancellation).
  1205  // If a connection has been delivered already, cancel returns it with t.putOrCloseIdleConn.
  1206  func (w *wantConn) cancel(t *Transport, err error) {
  1207  	w.mu.Lock()
  1208  	if w.pc == nil && w.err == nil {
  1209  		close(w.ready) // catch misbehavior in future delivery
  1210  	}
  1211  	pc := w.pc
  1212  	w.pc = nil
  1213  	w.err = err
  1214  	w.mu.Unlock()
  1215  
  1216  	if pc != nil {
  1217  		t.putOrCloseIdleConn(pc)
  1218  	}
  1219  }
  1220  
  1221  // A wantConnQueue is a queue of wantConns.
  1222  type wantConnQueue struct {
  1223  	// This is a queue, not a deque.
  1224  	// It is split into two stages - head[headPos:] and tail.
  1225  	// popFront is trivial (headPos++) on the first stage, and
  1226  	// pushBack is trivial (append) on the second stage.
  1227  	// If the first stage is empty, popFront can swap the
  1228  	// first and second stages to remedy the situation.
  1229  	//
  1230  	// This two-stage split is analogous to the use of two lists
  1231  	// in Okasaki's purely functional queue but without the
  1232  	// overhead of reversing the list when swapping stages.
  1233  	head    []*wantConn
  1234  	headPos int
  1235  	tail    []*wantConn
  1236  }
  1237  
  1238  // len returns the number of items in the queue.
  1239  func (q *wantConnQueue) len() int {
  1240  	return len(q.head) - q.headPos + len(q.tail)
  1241  }
  1242  
  1243  // pushBack adds w to the back of the queue.
  1244  func (q *wantConnQueue) pushBack(w *wantConn) {
  1245  	q.tail = append(q.tail, w)
  1246  }
  1247  
  1248  // popFront removes and returns the wantConn at the front of the queue.
  1249  func (q *wantConnQueue) popFront() *wantConn {
  1250  	if q.headPos >= len(q.head) {
  1251  		if len(q.tail) == 0 {
  1252  			return nil
  1253  		}
  1254  		// Pick up tail as new head, clear tail.
  1255  		q.head, q.headPos, q.tail = q.tail, 0, q.head[:0]
  1256  	}
  1257  	w := q.head[q.headPos]
  1258  	q.head[q.headPos] = nil
  1259  	q.headPos++
  1260  	return w
  1261  }
  1262  
  1263  // peekFront returns the wantConn at the front of the queue without removing it.
  1264  func (q *wantConnQueue) peekFront() *wantConn {
  1265  	if q.headPos < len(q.head) {
  1266  		return q.head[q.headPos]
  1267  	}
  1268  	if len(q.tail) > 0 {
  1269  		return q.tail[0]
  1270  	}
  1271  	return nil
  1272  }
  1273  
  1274  // cleanFront pops any wantConns that are no longer waiting from the head of the
  1275  // queue, reporting whether any were popped.
  1276  func (q *wantConnQueue) cleanFront() (cleaned bool) {
  1277  	for {
  1278  		w := q.peekFront()
  1279  		if w == nil || w.waiting() {
  1280  			return cleaned
  1281  		}
  1282  		q.popFront()
  1283  		cleaned = true
  1284  	}
  1285  }
  1286  
  1287  func (t *Transport) customDialTLS(ctx context.Context, network, addr string) (conn net.Conn, err error) {
  1288  	if t.DialTLSContext != nil {
  1289  		conn, err = t.DialTLSContext(ctx, network, addr)
  1290  	} else {
  1291  		conn, err = t.DialTLS(network, addr)
  1292  	}
  1293  	if conn == nil && err == nil {
  1294  		err = errors.New("net/http: Transport.DialTLS or DialTLSContext returned (nil, nil)")
  1295  	}
  1296  	return
  1297  }
  1298  
  1299  // getConn dials and creates a new persistConn to the target as
  1300  // specified in the connectMethod. This includes doing a proxy CONNECT
  1301  // and/or setting up TLS.  If this doesn't return an error, the persistConn
  1302  // is ready to write requests to.
  1303  func (t *Transport) getConn(treq *transportRequest, cm connectMethod) (pc *persistConn, err error) {
  1304  	req := treq.Request
  1305  	trace := treq.trace
  1306  	ctx := req.Context()
  1307  	if trace != nil && trace.GetConn != nil {
  1308  		trace.GetConn(cm.addr())
  1309  	}
  1310  
  1311  	w := &wantConn{
  1312  		cm:         cm,
  1313  		key:        cm.key(),
  1314  		ctx:        ctx,
  1315  		ready:      make(chan struct{}, 1),
  1316  		beforeDial: testHookPrePendingDial,
  1317  		afterDial:  testHookPostPendingDial,
  1318  	}
  1319  	defer func() {
  1320  		if err != nil {
  1321  			w.cancel(t, err)
  1322  		}
  1323  	}()
  1324  
  1325  	// Queue for idle connection.
  1326  	if delivered := t.queueForIdleConn(w); delivered {
  1327  		pc := w.pc
  1328  		// Trace only for HTTP/1.
  1329  		// HTTP/2 calls trace.GotConn itself.
  1330  		if pc.alt == nil && trace != nil && trace.GotConn != nil {
  1331  			trace.GotConn(pc.gotIdleConnTrace(pc.idleAt))
  1332  		}
  1333  		// set request canceler to some non-nil function so we
  1334  		// can detect whether it was cleared between now and when
  1335  		// we enter roundTrip
  1336  		t.setReqCanceler(treq.cancelKey, func(error) {})
  1337  		return pc, nil
  1338  	}
  1339  
  1340  	cancelc := make(chan error, 1)
  1341  	t.setReqCanceler(treq.cancelKey, func(err error) { cancelc <- err })
  1342  
  1343  	// Queue for permission to dial.
  1344  	t.queueForDial(w)
  1345  
  1346  	// Wait for completion or cancellation.
  1347  	select {
  1348  	case <-w.ready:
  1349  		// Trace success but only for HTTP/1.
  1350  		// HTTP/2 calls trace.GotConn itself.
  1351  		if w.pc != nil && w.pc.alt == nil && trace != nil && trace.GotConn != nil {
  1352  			trace.GotConn(httptrace.GotConnInfo{Conn: w.pc.conn, Reused: w.pc.isReused()})
  1353  		}
  1354  		if w.err != nil {
  1355  			// If the request has been cancelled, that's probably
  1356  			// what caused w.err; if so, prefer to return the
  1357  			// cancellation error (see golang.org/issue/16049).
  1358  			select {
  1359  			case <-req.Cancel:
  1360  				return nil, errRequestCanceledConn
  1361  			case <-req.Context().Done():
  1362  				return nil, req.Context().Err()
  1363  			case err := <-cancelc:
  1364  				if err == errRequestCanceled {
  1365  					err = errRequestCanceledConn
  1366  				}
  1367  				return nil, err
  1368  			default:
  1369  				// return below
  1370  			}
  1371  		}
  1372  		return w.pc, w.err
  1373  	case <-req.Cancel:
  1374  		return nil, errRequestCanceledConn
  1375  	case <-req.Context().Done():
  1376  		return nil, req.Context().Err()
  1377  	case err := <-cancelc:
  1378  		if err == errRequestCanceled {
  1379  			err = errRequestCanceledConn
  1380  		}
  1381  		return nil, err
  1382  	}
  1383  }
  1384  
  1385  // queueForDial queues w to wait for permission to begin dialing.
  1386  // Once w receives permission to dial, it will do so in a separate goroutine.
  1387  func (t *Transport) queueForDial(w *wantConn) {
  1388  	w.beforeDial()
  1389  	if t.MaxConnsPerHost <= 0 {
  1390  		go t.dialConnFor(w)
  1391  		return
  1392  	}
  1393  
  1394  	t.connsPerHostMu.Lock()
  1395  	defer t.connsPerHostMu.Unlock()
  1396  
  1397  	if n := t.connsPerHost[w.key]; n < t.MaxConnsPerHost {
  1398  		if t.connsPerHost == nil {
  1399  			t.connsPerHost = make(map[connectMethodKey]int)
  1400  		}
  1401  		t.connsPerHost[w.key] = n + 1
  1402  		go t.dialConnFor(w)
  1403  		return
  1404  	}
  1405  
  1406  	if t.connsPerHostWait == nil {
  1407  		t.connsPerHostWait = make(map[connectMethodKey]wantConnQueue)
  1408  	}
  1409  	q := t.connsPerHostWait[w.key]
  1410  	q.cleanFront()
  1411  	q.pushBack(w)
  1412  	t.connsPerHostWait[w.key] = q
  1413  }
  1414  
  1415  // dialConnFor dials on behalf of w and delivers the result to w.
  1416  // dialConnFor has received permission to dial w.cm and is counted in t.connCount[w.cm.key()].
  1417  // If the dial is cancelled or unsuccessful, dialConnFor decrements t.connCount[w.cm.key()].
  1418  func (t *Transport) dialConnFor(w *wantConn) {
  1419  	defer w.afterDial()
  1420  
  1421  	pc, err := t.dialConn(w.ctx, w.cm)
  1422  	delivered := w.tryDeliver(pc, err)
  1423  	if err == nil && (!delivered || pc.alt != nil) {
  1424  		// pconn was not passed to w,
  1425  		// or it is HTTP/2 and can be shared.
  1426  		// Add to the idle connection pool.
  1427  		t.putOrCloseIdleConn(pc)
  1428  	}
  1429  	if err != nil {
  1430  		t.decConnsPerHost(w.key)
  1431  	}
  1432  }
  1433  
  1434  // decConnsPerHost decrements the per-host connection count for key,
  1435  // which may in turn give a different waiting goroutine permission to dial.
  1436  func (t *Transport) decConnsPerHost(key connectMethodKey) {
  1437  	if t.MaxConnsPerHost <= 0 {
  1438  		return
  1439  	}
  1440  
  1441  	t.connsPerHostMu.Lock()
  1442  	defer t.connsPerHostMu.Unlock()
  1443  	n := t.connsPerHost[key]
  1444  	if n == 0 {
  1445  		// Shouldn't happen, but if it does, the counting is buggy and could
  1446  		// easily lead to a silent deadlock, so report the problem loudly.
  1447  		panic("net/http: internal error: connCount underflow")
  1448  	}
  1449  
  1450  	// Can we hand this count to a goroutine still waiting to dial?
  1451  	// (Some goroutines on the wait list may have timed out or
  1452  	// gotten a connection another way. If they're all gone,
  1453  	// we don't want to kick off any spurious dial operations.)
  1454  	if q := t.connsPerHostWait[key]; q.len() > 0 {
  1455  		done := false
  1456  		for q.len() > 0 {
  1457  			w := q.popFront()
  1458  			if w.waiting() {
  1459  				go t.dialConnFor(w)
  1460  				done = true
  1461  				break
  1462  			}
  1463  		}
  1464  		if q.len() == 0 {
  1465  			delete(t.connsPerHostWait, key)
  1466  		} else {
  1467  			// q is a value (like a slice), so we have to store
  1468  			// the updated q back into the map.
  1469  			t.connsPerHostWait[key] = q
  1470  		}
  1471  		if done {
  1472  			return
  1473  		}
  1474  	}
  1475  
  1476  	// Otherwise, decrement the recorded count.
  1477  	if n--; n == 0 {
  1478  		delete(t.connsPerHost, key)
  1479  	} else {
  1480  		t.connsPerHost[key] = n
  1481  	}
  1482  }
  1483  
  1484  // Add TLS to a persistent connection, i.e. negotiate a TLS session. If pconn is already a TLS
  1485  // tunnel, this function establishes a nested TLS session inside the encrypted channel.
  1486  // The remote endpoint's name may be overridden by TLSClientConfig.ServerName.
  1487  func (pconn *persistConn) addTLS(name string, trace *httptrace.ClientTrace) error {
  1488  	// Initiate TLS and check remote host name against certificate.
  1489  	cfg := cloneTLSConfig(pconn.t.TLSClientConfig)
  1490  	if cfg.ServerName == "" {
  1491  		cfg.ServerName = name
  1492  	}
  1493  	if pconn.cacheKey.onlyH1 {
  1494  		cfg.NextProtos = nil
  1495  	}
  1496  	plainConn := pconn.conn
  1497  	tlsConn := tls.Client(plainConn, cfg)
  1498  	errc := make(chan error, 2)
  1499  	var timer *time.Timer // for canceling TLS handshake
  1500  	if d := pconn.t.TLSHandshakeTimeout; d != 0 {
  1501  		timer = time.AfterFunc(d, func() {
  1502  			errc <- tlsHandshakeTimeoutError{}
  1503  		})
  1504  	}
  1505  	go func() {
  1506  		if trace != nil && trace.TLSHandshakeStart != nil {
  1507  			trace.TLSHandshakeStart()
  1508  		}
  1509  		err := tlsConn.Handshake()
  1510  		if timer != nil {
  1511  			timer.Stop()
  1512  		}
  1513  		errc <- err
  1514  	}()
  1515  	if err := <-errc; err != nil {
  1516  		plainConn.Close()
  1517  		if trace != nil && trace.TLSHandshakeDone != nil {
  1518  			trace.TLSHandshakeDone(tls.ConnectionState{}, err)
  1519  		}
  1520  		return err
  1521  	}
  1522  	cs := tlsConn.ConnectionState()
  1523  	if trace != nil && trace.TLSHandshakeDone != nil {
  1524  		trace.TLSHandshakeDone(cs, nil)
  1525  	}
  1526  	pconn.tlsState = &cs
  1527  	pconn.conn = tlsConn
  1528  	return nil
  1529  }
  1530  
  1531  func (t *Transport) dialConn(ctx context.Context, cm connectMethod) (pconn *persistConn, err error) {
  1532  	pconn = &persistConn{
  1533  		t:             t,
  1534  		cacheKey:      cm.key(),
  1535  		reqch:         make(chan requestAndChan, 1),
  1536  		writech:       make(chan writeRequest, 1),
  1537  		closech:       make(chan struct{}),
  1538  		writeErrCh:    make(chan error, 1),
  1539  		writeLoopDone: make(chan struct{}),
  1540  	}
  1541  	trace := httptrace.ContextClientTrace(ctx)
  1542  	wrapErr := func(err error) error {
  1543  		if cm.proxyURL != nil {
  1544  			// Return a typed error, per Issue 16997
  1545  			return &net.OpError{Op: "proxyconnect", Net: "tcp", Err: err}
  1546  		}
  1547  		return err
  1548  	}
  1549  	if cm.scheme() == "https" && t.hasCustomTLSDialer() {
  1550  		var err error
  1551  		pconn.conn, err = t.customDialTLS(ctx, "tcp", cm.addr())
  1552  		if err != nil {
  1553  			return nil, wrapErr(err)
  1554  		}
  1555  		if tc, ok := pconn.conn.(*tls.Conn); ok {
  1556  			// Handshake here, in case DialTLS didn't. TLSNextProto below
  1557  			// depends on it for knowing the connection state.
  1558  			if trace != nil && trace.TLSHandshakeStart != nil {
  1559  				trace.TLSHandshakeStart()
  1560  			}
  1561  			if err := tc.Handshake(); err != nil {
  1562  				go pconn.conn.Close()
  1563  				if trace != nil && trace.TLSHandshakeDone != nil {
  1564  					trace.TLSHandshakeDone(tls.ConnectionState{}, err)
  1565  				}
  1566  				return nil, err
  1567  			}
  1568  			cs := tc.ConnectionState()
  1569  			if trace != nil && trace.TLSHandshakeDone != nil {
  1570  				trace.TLSHandshakeDone(cs, nil)
  1571  			}
  1572  			pconn.tlsState = &cs
  1573  		}
  1574  	} else {
  1575  		conn, err := t.dial(ctx, "tcp", cm.addr())
  1576  		if err != nil {
  1577  			return nil, wrapErr(err)
  1578  		}
  1579  		pconn.conn = conn
  1580  		if cm.scheme() == "https" {
  1581  			var firstTLSHost string
  1582  			if firstTLSHost, _, err = net.SplitHostPort(cm.addr()); err != nil {
  1583  				return nil, wrapErr(err)
  1584  			}
  1585  			if err = pconn.addTLS(firstTLSHost, trace); err != nil {
  1586  				return nil, wrapErr(err)
  1587  			}
  1588  		}
  1589  	}
  1590  
  1591  	// Proxy setup.
  1592  	switch {
  1593  	case cm.proxyURL == nil:
  1594  		// Do nothing. Not using a proxy.
  1595  	case cm.proxyURL.Scheme == "socks5":
  1596  		conn := pconn.conn
  1597  		d := socksNewDialer("tcp", conn.RemoteAddr().String())
  1598  		if u := cm.proxyURL.User; u != nil {
  1599  			auth := &socksUsernamePassword{
  1600  				Username: u.Username(),
  1601  			}
  1602  			auth.Password, _ = u.Password()
  1603  			d.AuthMethods = []socksAuthMethod{
  1604  				socksAuthMethodNotRequired,
  1605  				socksAuthMethodUsernamePassword,
  1606  			}
  1607  			d.Authenticate = auth.Authenticate
  1608  		}
  1609  		if _, err := d.DialWithConn(ctx, conn, "tcp", cm.targetAddr); err != nil {
  1610  			conn.Close()
  1611  			return nil, err
  1612  		}
  1613  	case cm.targetScheme == "http":
  1614  		pconn.isProxy = true
  1615  		if pa := cm.proxyAuth(); pa != "" {
  1616  			pconn.mutateHeaderFunc = func(h Header) {
  1617  				h.Set("Proxy-Authorization", pa)
  1618  			}
  1619  		}
  1620  	case cm.targetScheme == "https":
  1621  		conn := pconn.conn
  1622  		hdr := t.ProxyConnectHeader
  1623  		if hdr == nil {
  1624  			hdr = make(Header)
  1625  		}
  1626  		if pa := cm.proxyAuth(); pa != "" {
  1627  			hdr = hdr.Clone()
  1628  			hdr.Set("Proxy-Authorization", pa)
  1629  		}
  1630  		connectReq := &Request{
  1631  			Method: "CONNECT",
  1632  			URL:    &url.URL{Opaque: cm.targetAddr},
  1633  			Host:   cm.targetAddr,
  1634  			Header: hdr,
  1635  		}
  1636  
  1637  		// If there's no done channel (no deadline or cancellation
  1638  		// from the caller possible), at least set some (long)
  1639  		// timeout here. This will make sure we don't block forever
  1640  		// and leak a goroutine if the connection stops replying
  1641  		// after the TCP connect.
  1642  		connectCtx := ctx
  1643  		if ctx.Done() == nil {
  1644  			newCtx, cancel := context.WithTimeout(ctx, 1*time.Minute)
  1645  			defer cancel()
  1646  			connectCtx = newCtx
  1647  		}
  1648  
  1649  		didReadResponse := make(chan struct{}) // closed after CONNECT write+read is done or fails
  1650  		var (
  1651  			resp *Response
  1652  			err  error // write or read error
  1653  		)
  1654  		// Write the CONNECT request & read the response.
  1655  		go func() {
  1656  			defer close(didReadResponse)
  1657  			err = connectReq.Write(conn)
  1658  			if err != nil {
  1659  				return
  1660  			}
  1661  			// Okay to use and discard buffered reader here, because
  1662  			// TLS server will not speak until spoken to.
  1663  			br := bufio.NewReader(conn)
  1664  			resp, err = ReadResponse(br, connectReq)
  1665  		}()
  1666  		select {
  1667  		case <-connectCtx.Done():
  1668  			conn.Close()
  1669  			<-didReadResponse
  1670  			return nil, connectCtx.Err()
  1671  		case <-didReadResponse:
  1672  			// resp or err now set
  1673  		}
  1674  		if err != nil {
  1675  			conn.Close()
  1676  			return nil, err
  1677  		}
  1678  		if resp.StatusCode != 200 {
  1679  			f := strings.SplitN(resp.Status, " ", 2)
  1680  			conn.Close()
  1681  			if len(f) < 2 {
  1682  				return nil, errors.New("unknown status code")
  1683  			}
  1684  			return nil, errors.New(f[1])
  1685  		}
  1686  	}
  1687  
  1688  	if cm.proxyURL != nil && cm.targetScheme == "https" {
  1689  		if err := pconn.addTLS(cm.tlsHost(), trace); err != nil {
  1690  			return nil, err
  1691  		}
  1692  	}
  1693  
  1694  	if s := pconn.tlsState; s != nil && s.NegotiatedProtocolIsMutual && s.NegotiatedProtocol != "" {
  1695  		if next, ok := t.TLSNextProto[s.NegotiatedProtocol]; ok {
  1696  			alt := next(cm.targetAddr, pconn.conn.(*tls.Conn))
  1697  			if e, ok := alt.(http2erringRoundTripper); ok {
  1698  				// pconn.conn was closed by next (http2configureTransport.upgradeFn).
  1699  				return nil, e.err
  1700  			}
  1701  			return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: alt}, nil
  1702  		}
  1703  	}
  1704  
  1705  	pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())
  1706  	pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())
  1707  
  1708  	go pconn.readLoop()
  1709  	go pconn.writeLoop()
  1710  	return pconn, nil
  1711  }
  1712  
  1713  // persistConnWriter is the io.Writer written to by pc.bw.
  1714  // It accumulates the number of bytes written to the underlying conn,
  1715  // so the retry logic can determine whether any bytes made it across
  1716  // the wire.
  1717  // This is exactly 1 pointer field wide so it can go into an interface
  1718  // without allocation.
  1719  type persistConnWriter struct {
  1720  	pc *persistConn
  1721  }
  1722  
  1723  func (w persistConnWriter) Write(p []byte) (n int, err error) {
  1724  	n, err = w.pc.conn.Write(p)
  1725  	w.pc.nwrite += int64(n)
  1726  	return
  1727  }
  1728  
  1729  // ReadFrom exposes persistConnWriter's underlying Conn to io.Copy and if
  1730  // the Conn implements io.ReaderFrom, it can take advantage of optimizations
  1731  // such as sendfile.
  1732  func (w persistConnWriter) ReadFrom(r io.Reader) (n int64, err error) {
  1733  	n, err = io.Copy(w.pc.conn, r)
  1734  	w.pc.nwrite += n
  1735  	return
  1736  }
  1737  
  1738  var _ io.ReaderFrom = (*persistConnWriter)(nil)
  1739  
  1740  // connectMethod is the map key (in its String form) for keeping persistent
  1741  // TCP connections alive for subsequent HTTP requests.
  1742  //
  1743  // A connect method may be of the following types:
  1744  //
  1745  //	connectMethod.key().String()      Description
  1746  //	------------------------------    -------------------------
  1747  //	|http|foo.com                     http directly to server, no proxy
  1748  //	|https|foo.com                    https directly to server, no proxy
  1749  //	|https,h1|foo.com                 https directly to server w/o HTTP/2, no proxy
  1750  //	http://proxy.com|https|foo.com    http to proxy, then CONNECT to foo.com
  1751  //	http://proxy.com|http             http to proxy, http to anywhere after that
  1752  //	socks5://proxy.com|http|foo.com   socks5 to proxy, then http to foo.com
  1753  //	socks5://proxy.com|https|foo.com  socks5 to proxy, then https to foo.com
  1754  //	https://proxy.com|https|foo.com   https to proxy, then CONNECT to foo.com
  1755  //	https://proxy.com|http            https to proxy, http to anywhere after that
  1756  //
  1757  type connectMethod struct {
  1758  	_            incomparable
  1759  	proxyURL     *url.URL // nil for no proxy, else full proxy URL
  1760  	targetScheme string   // "http" or "https"
  1761  	// If proxyURL specifies an http or https proxy, and targetScheme is http (not https),
  1762  	// then targetAddr is not included in the connect method key, because the socket can
  1763  	// be reused for different targetAddr values.
  1764  	targetAddr string
  1765  	onlyH1     bool // whether to disable HTTP/2 and force HTTP/1
  1766  }
  1767  
  1768  func (cm *connectMethod) key() connectMethodKey {
  1769  	proxyStr := ""
  1770  	targetAddr := cm.targetAddr
  1771  	if cm.proxyURL != nil {
  1772  		proxyStr = cm.proxyURL.String()
  1773  		if (cm.proxyURL.Scheme == "http" || cm.proxyURL.Scheme == "https") && cm.targetScheme == "http" {
  1774  			targetAddr = ""
  1775  		}
  1776  	}
  1777  	return connectMethodKey{
  1778  		proxy:  proxyStr,
  1779  		scheme: cm.targetScheme,
  1780  		addr:   targetAddr,
  1781  		onlyH1: cm.onlyH1,
  1782  	}
  1783  }
  1784  
  1785  // scheme returns the first hop scheme: http, https, or socks5
  1786  func (cm *connectMethod) scheme() string {
  1787  	if cm.proxyURL != nil {
  1788  		return cm.proxyURL.Scheme
  1789  	}
  1790  	return cm.targetScheme
  1791  }
  1792  
  1793  // addr returns the first hop "host:port" to which we need to TCP connect.
  1794  func (cm *connectMethod) addr() string {
  1795  	if cm.proxyURL != nil {
  1796  		return canonicalAddr(cm.proxyURL)
  1797  	}
  1798  	return cm.targetAddr
  1799  }
  1800  
  1801  // tlsHost returns the host name to match against the peer's
  1802  // TLS certificate.
  1803  func (cm *connectMethod) tlsHost() string {
  1804  	h := cm.targetAddr
  1805  	if hasPort(h) {
  1806  		h = h[:strings.LastIndex(h, ":")]
  1807  	}
  1808  	return h
  1809  }
  1810  
  1811  // connectMethodKey is the map key version of connectMethod, with a
  1812  // stringified proxy URL (or the empty string) instead of a pointer to
  1813  // a URL.
  1814  type connectMethodKey struct {
  1815  	proxy, scheme, addr string
  1816  	onlyH1              bool
  1817  }
  1818  
  1819  func (k connectMethodKey) String() string {
  1820  	// Only used by tests.
  1821  	var h1 string
  1822  	if k.onlyH1 {
  1823  		h1 = ",h1"
  1824  	}
  1825  	return fmt.Sprintf("%s|%s%s|%s", k.proxy, k.scheme, h1, k.addr)
  1826  }
  1827  
  1828  // persistConn wraps a connection, usually a persistent one
  1829  // (but may be used for non-keep-alive requests as well)
  1830  type persistConn struct {
  1831  	// alt optionally specifies the TLS NextProto RoundTripper.
  1832  	// This is used for HTTP/2 today and future protocols later.
  1833  	// If it's non-nil, the rest of the fields are unused.
  1834  	alt RoundTripper
  1835  
  1836  	t         *Transport
  1837  	cacheKey  connectMethodKey
  1838  	conn      net.Conn
  1839  	tlsState  *tls.ConnectionState
  1840  	br        *bufio.Reader       // from conn
  1841  	bw        *bufio.Writer       // to conn
  1842  	nwrite    int64               // bytes written
  1843  	reqch     chan requestAndChan // written by roundTrip; read by readLoop
  1844  	writech   chan writeRequest   // written by roundTrip; read by writeLoop
  1845  	closech   chan struct{}       // closed when conn closed
  1846  	isProxy   bool
  1847  	sawEOF    bool  // whether we've seen EOF from conn; owned by readLoop
  1848  	readLimit int64 // bytes allowed to be read; owned by readLoop
  1849  	// writeErrCh passes the request write error (usually nil)
  1850  	// from the writeLoop goroutine to the readLoop which passes
  1851  	// it off to the res.Body reader, which then uses it to decide
  1852  	// whether or not a connection can be reused. Issue 7569.
  1853  	writeErrCh chan error
  1854  
  1855  	writeLoopDone chan struct{} // closed when write loop ends
  1856  
  1857  	// Both guarded by Transport.idleMu:
  1858  	idleAt    time.Time   // time it last become idle
  1859  	idleTimer *time.Timer // holding an AfterFunc to close it
  1860  
  1861  	mu                   sync.Mutex // guards following fields
  1862  	numExpectedResponses int
  1863  	closed               error // set non-nil when conn is closed, before closech is closed
  1864  	canceledErr          error // set non-nil if conn is canceled
  1865  	broken               bool  // an error has happened on this connection; marked broken so it's not reused.
  1866  	reused               bool  // whether conn has had successful request/response and is being reused.
  1867  	// mutateHeaderFunc is an optional func to modify extra
  1868  	// headers on each outbound request before it's written. (the
  1869  	// original Request given to RoundTrip is not modified)
  1870  	mutateHeaderFunc func(Header)
  1871  }
  1872  
  1873  func (pc *persistConn) maxHeaderResponseSize() int64 {
  1874  	if v := pc.t.MaxResponseHeaderBytes; v != 0 {
  1875  		return v
  1876  	}
  1877  	return 10 << 20 // conservative default; same as http2
  1878  }
  1879  
  1880  func (pc *persistConn) Read(p []byte) (n int, err error) {
  1881  	if pc.readLimit <= 0 {
  1882  		return 0, fmt.Errorf("read limit of %d bytes exhausted", pc.maxHeaderResponseSize())
  1883  	}
  1884  	if int64(len(p)) > pc.readLimit {
  1885  		p = p[:pc.readLimit]
  1886  	}
  1887  	n, err = pc.conn.Read(p)
  1888  	if err == io.EOF {
  1889  		pc.sawEOF = true
  1890  	}
  1891  	pc.readLimit -= int64(n)
  1892  	return
  1893  }
  1894  
  1895  // isBroken reports whether this connection is in a known broken state.
  1896  func (pc *persistConn) isBroken() bool {
  1897  	pc.mu.Lock()
  1898  	b := pc.closed != nil
  1899  	pc.mu.Unlock()
  1900  	return b
  1901  }
  1902  
  1903  // canceled returns non-nil if the connection was closed due to
  1904  // CancelRequest or due to context cancellation.
  1905  func (pc *persistConn) canceled() error {
  1906  	pc.mu.Lock()
  1907  	defer pc.mu.Unlock()
  1908  	return pc.canceledErr
  1909  }
  1910  
  1911  // isReused reports whether this connection has been used before.
  1912  func (pc *persistConn) isReused() bool {
  1913  	pc.mu.Lock()
  1914  	r := pc.reused
  1915  	pc.mu.Unlock()
  1916  	return r
  1917  }
  1918  
  1919  func (pc *persistConn) gotIdleConnTrace(idleAt time.Time) (t httptrace.GotConnInfo) {
  1920  	pc.mu.Lock()
  1921  	defer pc.mu.Unlock()
  1922  	t.Reused = pc.reused
  1923  	t.Conn = pc.conn
  1924  	t.WasIdle = true
  1925  	if !idleAt.IsZero() {
  1926  		t.IdleTime = time.Since(idleAt)
  1927  	}
  1928  	return
  1929  }
  1930  
  1931  func (pc *persistConn) cancelRequest(err error) {
  1932  	pc.mu.Lock()
  1933  	defer pc.mu.Unlock()
  1934  	pc.canceledErr = err
  1935  	pc.closeLocked(errRequestCanceled)
  1936  }
  1937  
  1938  // closeConnIfStillIdle closes the connection if it's still sitting idle.
  1939  // This is what's called by the persistConn's idleTimer, and is run in its
  1940  // own goroutine.
  1941  func (pc *persistConn) closeConnIfStillIdle() {
  1942  	t := pc.t
  1943  	t.idleMu.Lock()
  1944  	defer t.idleMu.Unlock()
  1945  	if _, ok := t.idleLRU.m[pc]; !ok {
  1946  		// Not idle.
  1947  		return
  1948  	}
  1949  	t.removeIdleConnLocked(pc)
  1950  	pc.close(errIdleConnTimeout)
  1951  }
  1952  
  1953  // mapRoundTripError returns the appropriate error value for
  1954  // persistConn.roundTrip.
  1955  //
  1956  // The provided err is the first error that (*persistConn).roundTrip
  1957  // happened to receive from its select statement.
  1958  //
  1959  // The startBytesWritten value should be the value of pc.nwrite before the roundTrip
  1960  // started writing the request.
  1961  func (pc *persistConn) mapRoundTripError(req *transportRequest, startBytesWritten int64, err error) error {
  1962  	if err == nil {
  1963  		return nil
  1964  	}
  1965  
  1966  	// If the request was canceled, that's better than network
  1967  	// failures that were likely the result of tearing down the
  1968  	// connection.
  1969  	if cerr := pc.canceled(); cerr != nil {
  1970  		return cerr
  1971  	}
  1972  
  1973  	// See if an error was set explicitly.
  1974  	req.mu.Lock()
  1975  	reqErr := req.err
  1976  	req.mu.Unlock()
  1977  	if reqErr != nil {
  1978  		return reqErr
  1979  	}
  1980  
  1981  	if err == errServerClosedIdle {
  1982  		// Don't decorate
  1983  		return err
  1984  	}
  1985  
  1986  	if _, ok := err.(transportReadFromServerError); ok {
  1987  		// Don't decorate
  1988  		return err
  1989  	}
  1990  	if pc.isBroken() {
  1991  		<-pc.writeLoopDone
  1992  		if pc.nwrite == startBytesWritten {
  1993  			return nothingWrittenError{err}
  1994  		}
  1995  		return fmt.Errorf("net/http: HTTP/1.x transport connection broken: %v", err)
  1996  	}
  1997  	return err
  1998  }
  1999  
  2000  // errCallerOwnsConn is an internal sentinel error used when we hand
  2001  // off a writable response.Body to the caller. We use this to prevent
  2002  // closing a net.Conn that is now owned by the caller.
  2003  var errCallerOwnsConn = errors.New("read loop ending; caller owns writable underlying conn")
  2004  
  2005  func (pc *persistConn) readLoop() {
  2006  	closeErr := errReadLoopExiting // default value, if not changed below
  2007  	defer func() {
  2008  		pc.close(closeErr)
  2009  		pc.t.removeIdleConn(pc)
  2010  	}()
  2011  
  2012  	tryPutIdleConn := func(trace *httptrace.ClientTrace) bool {
  2013  		if err := pc.t.tryPutIdleConn(pc); err != nil {
  2014  			closeErr = err
  2015  			if trace != nil && trace.PutIdleConn != nil && err != errKeepAlivesDisabled {
  2016  				trace.PutIdleConn(err)
  2017  			}
  2018  			return false
  2019  		}
  2020  		if trace != nil && trace.PutIdleConn != nil {
  2021  			trace.PutIdleConn(nil)
  2022  		}
  2023  		return true
  2024  	}
  2025  
  2026  	// eofc is used to block caller goroutines reading from Response.Body
  2027  	// at EOF until this goroutines has (potentially) added the connection
  2028  	// back to the idle pool.
  2029  	eofc := make(chan struct{})
  2030  	defer close(eofc) // unblock reader on errors
  2031  
  2032  	// Read this once, before loop starts. (to avoid races in tests)
  2033  	testHookMu.Lock()
  2034  	testHookReadLoopBeforeNextRead := testHookReadLoopBeforeNextRead
  2035  	testHookMu.Unlock()
  2036  
  2037  	alive := true
  2038  	for alive {
  2039  		pc.readLimit = pc.maxHeaderResponseSize()
  2040  		_, err := pc.br.Peek(1)
  2041  
  2042  		pc.mu.Lock()
  2043  		if pc.numExpectedResponses == 0 {
  2044  			pc.readLoopPeekFailLocked(err)
  2045  			pc.mu.Unlock()
  2046  			return
  2047  		}
  2048  		pc.mu.Unlock()
  2049  
  2050  		rc := <-pc.reqch
  2051  		trace := httptrace.ContextClientTrace(rc.req.Context())
  2052  
  2053  		var resp *Response
  2054  		if err == nil {
  2055  			resp, err = pc.readResponse(rc, trace)
  2056  		} else {
  2057  			err = transportReadFromServerError{err}
  2058  			closeErr = err
  2059  		}
  2060  
  2061  		if err != nil {
  2062  			if pc.readLimit <= 0 {
  2063  				err = fmt.Errorf("net/http: server response headers exceeded %d bytes; aborted", pc.maxHeaderResponseSize())
  2064  			}
  2065  
  2066  			select {
  2067  			case rc.ch <- responseAndError{err: err}:
  2068  			case <-rc.callerGone:
  2069  				return
  2070  			}
  2071  			return
  2072  		}
  2073  		pc.readLimit = maxInt64 // effectively no limit for response bodies
  2074  
  2075  		pc.mu.Lock()
  2076  		pc.numExpectedResponses--
  2077  		pc.mu.Unlock()
  2078  
  2079  		bodyWritable := resp.bodyIsWritable()
  2080  		hasBody := rc.req.Method != "HEAD" && resp.ContentLength != 0
  2081  
  2082  		if resp.Close || rc.req.Close || resp.StatusCode <= 199 || bodyWritable {
  2083  			// Don't do keep-alive on error if either party requested a close
  2084  			// or we get an unexpected informational (1xx) response.
  2085  			// StatusCode 100 is already handled above.
  2086  			alive = false
  2087  		}
  2088  
  2089  		if !hasBody || bodyWritable {
  2090  			pc.t.setReqCanceler(rc.cancelKey, nil)
  2091  
  2092  			// Put the idle conn back into the pool before we send the response
  2093  			// so if they process it quickly and make another request, they'll
  2094  			// get this same conn. But we use the unbuffered channel 'rc'
  2095  			// to guarantee that persistConn.roundTrip got out of its select
  2096  			// potentially waiting for this persistConn to close.
  2097  			// but after
  2098  			alive = alive &&
  2099  				!pc.sawEOF &&
  2100  				pc.wroteRequest() &&
  2101  				tryPutIdleConn(trace)
  2102  
  2103  			if bodyWritable {
  2104  				closeErr = errCallerOwnsConn
  2105  			}
  2106  
  2107  			select {
  2108  			case rc.ch <- responseAndError{res: resp}:
  2109  			case <-rc.callerGone:
  2110  				return
  2111  			}
  2112  
  2113  			// Now that they've read from the unbuffered channel, they're safely
  2114  			// out of the select that also waits on this goroutine to die, so
  2115  			// we're allowed to exit now if needed (if alive is false)
  2116  			testHookReadLoopBeforeNextRead()
  2117  			continue
  2118  		}
  2119  
  2120  		waitForBodyRead := make(chan bool, 2)
  2121  		body := &bodyEOFSignal{
  2122  			body: resp.Body,
  2123  			earlyCloseFn: func() error {
  2124  				waitForBodyRead <- false
  2125  				<-eofc // will be closed by deferred call at the end of the function
  2126  				return nil
  2127  
  2128  			},
  2129  			fn: func(err error) error {
  2130  				isEOF := err == io.EOF
  2131  				waitForBodyRead <- isEOF
  2132  				if isEOF {
  2133  					<-eofc // see comment above eofc declaration
  2134  				} else if err != nil {
  2135  					if cerr := pc.canceled(); cerr != nil {
  2136  						return cerr
  2137  					}
  2138  				}
  2139  				return err
  2140  			},
  2141  		}
  2142  
  2143  		resp.Body = body
  2144  		if rc.addedGzip && strings.EqualFold(resp.Header.Get("Content-Encoding"), "gzip") {
  2145  			resp.Body = &gzipReader{body: body}
  2146  			resp.Header.Del("Content-Encoding")
  2147  			resp.Header.Del("Content-Length")
  2148  			resp.ContentLength = -1
  2149  			resp.Uncompressed = true
  2150  		}
  2151  
  2152  		select {
  2153  		case rc.ch <- responseAndError{res: resp}:
  2154  		case <-rc.callerGone:
  2155  			return
  2156  		}
  2157  
  2158  		// Before looping back to the top of this function and peeking on
  2159  		// the bufio.Reader, wait for the caller goroutine to finish
  2160  		// reading the response body. (or for cancellation or death)
  2161  		select {
  2162  		case bodyEOF := <-waitForBodyRead:
  2163  			pc.t.setReqCanceler(rc.cancelKey, nil) // before pc might return to idle pool
  2164  			alive = alive &&
  2165  				bodyEOF &&
  2166  				!pc.sawEOF &&
  2167  				pc.wroteRequest() &&
  2168  				tryPutIdleConn(trace)
  2169  			if bodyEOF {
  2170  				eofc <- struct{}{}
  2171  			}
  2172  		case <-rc.req.Cancel:
  2173  			alive = false
  2174  			pc.t.CancelRequest(rc.req)
  2175  		case <-rc.req.Context().Done():
  2176  			alive = false
  2177  			pc.t.cancelRequest(rc.cancelKey, rc.req.Context().Err())
  2178  		case <-pc.closech:
  2179  			alive = false
  2180  		}
  2181  
  2182  		testHookReadLoopBeforeNextRead()
  2183  	}
  2184  }
  2185  
  2186  func (pc *persistConn) readLoopPeekFailLocked(peekErr error) {
  2187  	if pc.closed != nil {
  2188  		return
  2189  	}
  2190  	if n := pc.br.Buffered(); n > 0 {
  2191  		buf, _ := pc.br.Peek(n)
  2192  		if is408Message(buf) {
  2193  			pc.closeLocked(errServerClosedIdle)
  2194  			return
  2195  		} else {
  2196  			log.Printf("Unsolicited response received on idle HTTP channel starting with %q; err=%v", buf, peekErr)
  2197  		}
  2198  	}
  2199  	if peekErr == io.EOF {
  2200  		// common case.
  2201  		pc.closeLocked(errServerClosedIdle)
  2202  	} else {
  2203  		pc.closeLocked(fmt.Errorf("readLoopPeekFailLocked: %v", peekErr))
  2204  	}
  2205  }
  2206  
  2207  // is408Message reports whether buf has the prefix of an
  2208  // HTTP 408 Request Timeout response.
  2209  // See golang.org/issue/32310.
  2210  func is408Message(buf []byte) bool {
  2211  	if len(buf) < len("HTTP/1.x 408") {
  2212  		return false
  2213  	}
  2214  	if string(buf[:7]) != "HTTP/1." {
  2215  		return false
  2216  	}
  2217  	return string(buf[8:12]) == " 408"
  2218  }
  2219  
  2220  // readResponse reads an HTTP response (or two, in the case of "Expect:
  2221  // 100-continue") from the server. It returns the final non-100 one.
  2222  // trace is optional.
  2223  func (pc *persistConn) readResponse(rc requestAndChan, trace *httptrace.ClientTrace) (resp *Response, err error) {
  2224  	if trace != nil && trace.GotFirstResponseByte != nil {
  2225  		if peek, err := pc.br.Peek(1); err == nil && len(peek) == 1 {
  2226  			trace.GotFirstResponseByte()
  2227  		}
  2228  	}
  2229  	num1xx := 0               // number of informational 1xx headers received
  2230  	const max1xxResponses = 5 // arbitrary bound on number of informational responses
  2231  
  2232  	continueCh := rc.continueCh
  2233  	for {
  2234  		resp, err = ReadResponse(pc.br, rc.req)
  2235  		if err != nil {
  2236  			return
  2237  		}
  2238  		resCode := resp.StatusCode
  2239  		if continueCh != nil {
  2240  			if resCode == 100 {
  2241  				if trace != nil && trace.Got100Continue != nil {
  2242  					trace.Got100Continue()
  2243  				}
  2244  				continueCh <- struct{}{}
  2245  				continueCh = nil
  2246  			} else if resCode >= 200 {
  2247  				close(continueCh)
  2248  				continueCh = nil
  2249  			}
  2250  		}
  2251  		is1xx := 100 <= resCode && resCode <= 199
  2252  		// treat 101 as a terminal status, see issue 26161
  2253  		is1xxNonTerminal := is1xx && resCode != StatusSwitchingProtocols
  2254  		if is1xxNonTerminal {
  2255  			num1xx++
  2256  			if num1xx > max1xxResponses {
  2257  				return nil, errors.New("net/http: too many 1xx informational responses")
  2258  			}
  2259  			pc.readLimit = pc.maxHeaderResponseSize() // reset the limit
  2260  			if trace != nil && trace.Got1xxResponse != nil {
  2261  				if err := trace.Got1xxResponse(resCode, textproto.MIMEHeader(resp.Header)); err != nil {
  2262  					return nil, err
  2263  				}
  2264  			}
  2265  			continue
  2266  		}
  2267  		break
  2268  	}
  2269  	if resp.isProtocolSwitch() {
  2270  		resp.Body = newReadWriteCloserBody(pc.br, pc.conn)
  2271  	}
  2272  
  2273  	resp.TLS = pc.tlsState
  2274  	return
  2275  }
  2276  
  2277  // waitForContinue returns the function to block until
  2278  // any response, timeout or connection close. After any of them,
  2279  // the function returns a bool which indicates if the body should be sent.
  2280  func (pc *persistConn) waitForContinue(continueCh <-chan struct{}) func() bool {
  2281  	if continueCh == nil {
  2282  		return nil
  2283  	}
  2284  	return func() bool {
  2285  		timer := time.NewTimer(pc.t.ExpectContinueTimeout)
  2286  		defer timer.Stop()
  2287  
  2288  		select {
  2289  		case _, ok := <-continueCh:
  2290  			return ok
  2291  		case <-timer.C:
  2292  			return true
  2293  		case <-pc.closech:
  2294  			return false
  2295  		}
  2296  	}
  2297  }
  2298  
  2299  func newReadWriteCloserBody(br *bufio.Reader, rwc io.ReadWriteCloser) io.ReadWriteCloser {
  2300  	body := &readWriteCloserBody{ReadWriteCloser: rwc}
  2301  	if br.Buffered() != 0 {
  2302  		body.br = br
  2303  	}
  2304  	return body
  2305  }
  2306  
  2307  // readWriteCloserBody is the Response.Body type used when we want to
  2308  // give users write access to the Body through the underlying
  2309  // connection (TCP, unless using custom dialers). This is then
  2310  // the concrete type for a Response.Body on the 101 Switching
  2311  // Protocols response, as used by WebSockets, h2c, etc.
  2312  type readWriteCloserBody struct {
  2313  	_  incomparable
  2314  	br *bufio.Reader // used until empty
  2315  	io.ReadWriteCloser
  2316  }
  2317  
  2318  func (b *readWriteCloserBody) Read(p []byte) (n int, err error) {
  2319  	if b.br != nil {
  2320  		if n := b.br.Buffered(); len(p) > n {
  2321  			p = p[:n]
  2322  		}
  2323  		n, err = b.br.Read(p)
  2324  		if b.br.Buffered() == 0 {
  2325  			b.br = nil
  2326  		}
  2327  		return n, err
  2328  	}
  2329  	return b.ReadWriteCloser.Read(p)
  2330  }
  2331  
  2332  // nothingWrittenError wraps a write errors which ended up writing zero bytes.
  2333  type nothingWrittenError struct {
  2334  	error
  2335  }
  2336  
  2337  func (pc *persistConn) writeLoop() {
  2338  	defer close(pc.writeLoopDone)
  2339  	for {
  2340  		select {
  2341  		case wr := <-pc.writech:
  2342  			startBytesWritten := pc.nwrite
  2343  			err := wr.req.Request.write(pc.bw, pc.isProxy, wr.req.extra, pc.waitForContinue(wr.continueCh))
  2344  			if bre, ok := err.(requestBodyReadError); ok {
  2345  				err = bre.error
  2346  				// Errors reading from the user's
  2347  				// Request.Body are high priority.
  2348  				// Set it here before sending on the
  2349  				// channels below or calling
  2350  				// pc.close() which tears town
  2351  				// connections and causes other
  2352  				// errors.
  2353  				wr.req.setError(err)
  2354  			}
  2355  			if err == nil {
  2356  				err = pc.bw.Flush()
  2357  			}
  2358  			if err != nil {
  2359  				wr.req.Request.closeBody()
  2360  				if pc.nwrite == startBytesWritten {
  2361  					err = nothingWrittenError{err}
  2362  				}
  2363  			}
  2364  			pc.writeErrCh <- err // to the body reader, which might recycle us
  2365  			wr.ch <- err         // to the roundTrip function
  2366  			if err != nil {
  2367  				pc.close(err)
  2368  				return
  2369  			}
  2370  		case <-pc.closech:
  2371  			return
  2372  		}
  2373  	}
  2374  }
  2375  
  2376  // maxWriteWaitBeforeConnReuse is how long the a Transport RoundTrip
  2377  // will wait to see the Request's Body.Write result after getting a
  2378  // response from the server. See comments in (*persistConn).wroteRequest.
  2379  const maxWriteWaitBeforeConnReuse = 50 * time.Millisecond
  2380  
  2381  // wroteRequest is a check before recycling a connection that the previous write
  2382  // (from writeLoop above) happened and was successful.
  2383  func (pc *persistConn) wroteRequest() bool {
  2384  	select {
  2385  	case err := <-pc.writeErrCh:
  2386  		// Common case: the write happened well before the response, so
  2387  		// avoid creating a timer.
  2388  		return err == nil
  2389  	default:
  2390  		// Rare case: the request was written in writeLoop above but
  2391  		// before it could send to pc.writeErrCh, the reader read it
  2392  		// all, processed it, and called us here. In this case, give the
  2393  		// write goroutine a bit of time to finish its send.
  2394  		//
  2395  		// Less rare case: We also get here in the legitimate case of
  2396  		// Issue 7569, where the writer is still writing (or stalled),
  2397  		// but the server has already replied. In this case, we don't
  2398  		// want to wait too long, and we want to return false so this
  2399  		// connection isn't re-used.
  2400  		t := time.NewTimer(maxWriteWaitBeforeConnReuse)
  2401  		defer t.Stop()
  2402  		select {
  2403  		case err := <-pc.writeErrCh:
  2404  			return err == nil
  2405  		case <-t.C:
  2406  			return false
  2407  		}
  2408  	}
  2409  }
  2410  
  2411  // responseAndError is how the goroutine reading from an HTTP/1 server
  2412  // communicates with the goroutine doing the RoundTrip.
  2413  type responseAndError struct {
  2414  	_   incomparable
  2415  	res *Response // else use this response (see res method)
  2416  	err error
  2417  }
  2418  
  2419  type requestAndChan struct {
  2420  	_         incomparable
  2421  	req       *Request
  2422  	cancelKey cancelKey
  2423  	ch        chan responseAndError // unbuffered; always send in select on callerGone
  2424  
  2425  	// whether the Transport (as opposed to the user client code)
  2426  	// added the Accept-Encoding gzip header. If the Transport
  2427  	// set it, only then do we transparently decode the gzip.
  2428  	addedGzip bool
  2429  
  2430  	// Optional blocking chan for Expect: 100-continue (for send).
  2431  	// If the request has an "Expect: 100-continue" header and
  2432  	// the server responds 100 Continue, readLoop send a value
  2433  	// to writeLoop via this chan.
  2434  	continueCh chan<- struct{}
  2435  
  2436  	callerGone <-chan struct{} // closed when roundTrip caller has returned
  2437  }
  2438  
  2439  // A writeRequest is sent by the readLoop's goroutine to the
  2440  // writeLoop's goroutine to write a request while the read loop
  2441  // concurrently waits on both the write response and the server's
  2442  // reply.
  2443  type writeRequest struct {
  2444  	req *transportRequest
  2445  	ch  chan<- error
  2446  
  2447  	// Optional blocking chan for Expect: 100-continue (for receive).
  2448  	// If not nil, writeLoop blocks sending request body until
  2449  	// it receives from this chan.
  2450  	continueCh <-chan struct{}
  2451  }
  2452  
  2453  type httpError struct {
  2454  	err     string
  2455  	timeout bool
  2456  }
  2457  
  2458  func (e *httpError) Error() string   { return e.err }
  2459  func (e *httpError) Timeout() bool   { return e.timeout }
  2460  func (e *httpError) Temporary() bool { return true }
  2461  
  2462  var errTimeout error = &httpError{err: "net/http: timeout awaiting response headers", timeout: true}
  2463  
  2464  // errRequestCanceled is set to be identical to the one from h2 to facilitate
  2465  // testing.
  2466  var errRequestCanceled = http2errRequestCanceled
  2467  var errRequestCanceledConn = errors.New("net/http: request canceled while waiting for connection") // TODO: unify?
  2468  
  2469  func nop() {}
  2470  
  2471  // testHooks. Always non-nil.
  2472  var (
  2473  	testHookEnterRoundTrip   = nop
  2474  	testHookWaitResLoop      = nop
  2475  	testHookRoundTripRetried = nop
  2476  	testHookPrePendingDial   = nop
  2477  	testHookPostPendingDial  = nop
  2478  
  2479  	testHookMu                     sync.Locker = fakeLocker{} // guards following
  2480  	testHookReadLoopBeforeNextRead             = nop
  2481  )
  2482  
  2483  func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) {
  2484  	testHookEnterRoundTrip()
  2485  	if !pc.t.replaceReqCanceler(req.cancelKey, pc.cancelRequest) {
  2486  		pc.t.putOrCloseIdleConn(pc)
  2487  		return nil, errRequestCanceled
  2488  	}
  2489  	pc.mu.Lock()
  2490  	pc.numExpectedResponses++
  2491  	headerFn := pc.mutateHeaderFunc
  2492  	pc.mu.Unlock()
  2493  
  2494  	if headerFn != nil {
  2495  		headerFn(req.extraHeaders())
  2496  	}
  2497  
  2498  	// Ask for a compressed version if the caller didn't set their
  2499  	// own value for Accept-Encoding. We only attempt to
  2500  	// uncompress the gzip stream if we were the layer that
  2501  	// requested it.
  2502  	requestedGzip := false
  2503  	if !pc.t.DisableCompression &&
  2504  		req.Header.Get("Accept-Encoding") == "" &&
  2505  		req.Header.Get("Range") == "" &&
  2506  		req.Method != "HEAD" {
  2507  		// Request gzip only, not deflate. Deflate is ambiguous and
  2508  		// not as universally supported anyway.
  2509  		// See: https://zlib.net/zlib_faq.html#faq39
  2510  		//
  2511  		// Note that we don't request this for HEAD requests,
  2512  		// due to a bug in nginx:
  2513  		//   https://trac.nginx.org/nginx/ticket/358
  2514  		//   https://golang.org/issue/5522
  2515  		//
  2516  		// We don't request gzip if the request is for a range, since
  2517  		// auto-decoding a portion of a gzipped document will just fail
  2518  		// anyway. See https://golang.org/issue/8923
  2519  		requestedGzip = true
  2520  		req.extraHeaders().Set("Accept-Encoding", "gzip")
  2521  	}
  2522  
  2523  	var continueCh chan struct{}
  2524  	if req.ProtoAtLeast(1, 1) && req.Body != nil && req.expectsContinue() {
  2525  		continueCh = make(chan struct{}, 1)
  2526  	}
  2527  
  2528  	if pc.t.DisableKeepAlives && !req.wantsClose() {
  2529  		req.extraHeaders().Set("Connection", "close")
  2530  	}
  2531  
  2532  	gone := make(chan struct{})
  2533  	defer close(gone)
  2534  
  2535  	defer func() {
  2536  		if err != nil {
  2537  			pc.t.setReqCanceler(req.cancelKey, nil)
  2538  		}
  2539  	}()
  2540  
  2541  	const debugRoundTrip = false
  2542  
  2543  	// Write the request concurrently with waiting for a response,
  2544  	// in case the server decides to reply before reading our full
  2545  	// request body.
  2546  	startBytesWritten := pc.nwrite
  2547  	writeErrCh := make(chan error, 1)
  2548  	pc.writech <- writeRequest{req, writeErrCh, continueCh}
  2549  
  2550  	resc := make(chan responseAndError)
  2551  	pc.reqch <- requestAndChan{
  2552  		req:        req.Request,
  2553  		cancelKey:  req.cancelKey,
  2554  		ch:         resc,
  2555  		addedGzip:  requestedGzip,
  2556  		continueCh: continueCh,
  2557  		callerGone: gone,
  2558  	}
  2559  
  2560  	var respHeaderTimer <-chan time.Time
  2561  	cancelChan := req.Request.Cancel
  2562  	ctxDoneChan := req.Context().Done()
  2563  	for {
  2564  		testHookWaitResLoop()
  2565  		select {
  2566  		case err := <-writeErrCh:
  2567  			if debugRoundTrip {
  2568  				req.logf("writeErrCh resv: %T/%#v", err, err)
  2569  			}
  2570  			if err != nil {
  2571  				pc.close(fmt.Errorf("write error: %v", err))
  2572  				return nil, pc.mapRoundTripError(req, startBytesWritten, err)
  2573  			}
  2574  			if d := pc.t.ResponseHeaderTimeout; d > 0 {
  2575  				if debugRoundTrip {
  2576  					req.logf("starting timer for %v", d)
  2577  				}
  2578  				timer := time.NewTimer(d)
  2579  				defer timer.Stop() // prevent leaks
  2580  				respHeaderTimer = timer.C
  2581  			}
  2582  		case <-pc.closech:
  2583  			if debugRoundTrip {
  2584  				req.logf("closech recv: %T %#v", pc.closed, pc.closed)
  2585  			}
  2586  			return nil, pc.mapRoundTripError(req, startBytesWritten, pc.closed)
  2587  		case <-respHeaderTimer:
  2588  			if debugRoundTrip {
  2589  				req.logf("timeout waiting for response headers.")
  2590  			}
  2591  			pc.close(errTimeout)
  2592  			return nil, errTimeout
  2593  		case re := <-resc:
  2594  			if (re.res == nil) == (re.err == nil) {
  2595  				panic(fmt.Sprintf("internal error: exactly one of res or err should be set; nil=%v", re.res == nil))
  2596  			}
  2597  			if debugRoundTrip {
  2598  				req.logf("resc recv: %p, %T/%#v", re.res, re.err, re.err)
  2599  			}
  2600  			if re.err != nil {
  2601  				return nil, pc.mapRoundTripError(req, startBytesWritten, re.err)
  2602  			}
  2603  			return re.res, nil
  2604  		case <-cancelChan:
  2605  			pc.t.cancelRequest(req.cancelKey, errRequestCanceled)
  2606  			cancelChan = nil
  2607  		case <-ctxDoneChan:
  2608  			pc.t.cancelRequest(req.cancelKey, req.Context().Err())
  2609  			cancelChan = nil
  2610  			ctxDoneChan = nil
  2611  		}
  2612  	}
  2613  }
  2614  
  2615  // tLogKey is a context WithValue key for test debugging contexts containing
  2616  // a t.Logf func. See export_test.go's Request.WithT method.
  2617  type tLogKey struct{}
  2618  
  2619  func (tr *transportRequest) logf(format string, args ...interface{}) {
  2620  	if logf, ok := tr.Request.Context().Value(tLogKey{}).(func(string, ...interface{})); ok {
  2621  		logf(time.Now().Format(time.RFC3339Nano)+": "+format, args...)
  2622  	}
  2623  }
  2624  
  2625  // markReused marks this connection as having been successfully used for a
  2626  // request and response.
  2627  func (pc *persistConn) markReused() {
  2628  	pc.mu.Lock()
  2629  	pc.reused = true
  2630  	pc.mu.Unlock()
  2631  }
  2632  
  2633  // close closes the underlying TCP connection and closes
  2634  // the pc.closech channel.
  2635  //
  2636  // The provided err is only for testing and debugging; in normal
  2637  // circumstances it should never be seen by users.
  2638  func (pc *persistConn) close(err error) {
  2639  	pc.mu.Lock()
  2640  	defer pc.mu.Unlock()
  2641  	pc.closeLocked(err)
  2642  }
  2643  
  2644  func (pc *persistConn) closeLocked(err error) {
  2645  	if err == nil {
  2646  		panic("nil error")
  2647  	}
  2648  	pc.broken = true
  2649  	if pc.closed == nil {
  2650  		pc.closed = err
  2651  		pc.t.decConnsPerHost(pc.cacheKey)
  2652  		// Close HTTP/1 (pc.alt == nil) connection.
  2653  		// HTTP/2 closes its connection itself.
  2654  		if pc.alt == nil {
  2655  			if err != errCallerOwnsConn {
  2656  				pc.conn.Close()
  2657  			}
  2658  			close(pc.closech)
  2659  		}
  2660  	}
  2661  	pc.mutateHeaderFunc = nil
  2662  }
  2663  
  2664  var portMap = map[string]string{
  2665  	"http":   "80",
  2666  	"https":  "443",
  2667  	"socks5": "1080",
  2668  }
  2669  
  2670  // canonicalAddr returns url.Host but always with a ":port" suffix
  2671  func canonicalAddr(url *url.URL) string {
  2672  	addr := url.Hostname()
  2673  	if v, err := idnaASCII(addr); err == nil {
  2674  		addr = v
  2675  	}
  2676  	port := url.Port()
  2677  	if port == "" {
  2678  		port = portMap[url.Scheme]
  2679  	}
  2680  	return net.JoinHostPort(addr, port)
  2681  }
  2682  
  2683  // bodyEOFSignal is used by the HTTP/1 transport when reading response
  2684  // bodies to make sure we see the end of a response body before
  2685  // proceeding and reading on the connection again.
  2686  //
  2687  // It wraps a ReadCloser but runs fn (if non-nil) at most
  2688  // once, right before its final (error-producing) Read or Close call
  2689  // returns. fn should return the new error to return from Read or Close.
  2690  //
  2691  // If earlyCloseFn is non-nil and Close is called before io.EOF is
  2692  // seen, earlyCloseFn is called instead of fn, and its return value is
  2693  // the return value from Close.
  2694  type bodyEOFSignal struct {
  2695  	body         io.ReadCloser
  2696  	mu           sync.Mutex        // guards following 4 fields
  2697  	closed       bool              // whether Close has been called
  2698  	rerr         error             // sticky Read error
  2699  	fn           func(error) error // err will be nil on Read io.EOF
  2700  	earlyCloseFn func() error      // optional alt Close func used if io.EOF not seen
  2701  }
  2702  
  2703  var errReadOnClosedResBody = errors.New("http: read on closed response body")
  2704  
  2705  func (es *bodyEOFSignal) Read(p []byte) (n int, err error) {
  2706  	es.mu.Lock()
  2707  	closed, rerr := es.closed, es.rerr
  2708  	es.mu.Unlock()
  2709  	if closed {
  2710  		return 0, errReadOnClosedResBody
  2711  	}
  2712  	if rerr != nil {
  2713  		return 0, rerr
  2714  	}
  2715  
  2716  	n, err = es.body.Read(p)
  2717  	if err != nil {
  2718  		es.mu.Lock()
  2719  		defer es.mu.Unlock()
  2720  		if es.rerr == nil {
  2721  			es.rerr = err
  2722  		}
  2723  		err = es.condfn(err)
  2724  	}
  2725  	return
  2726  }
  2727  
  2728  func (es *bodyEOFSignal) Close() error {
  2729  	es.mu.Lock()
  2730  	defer es.mu.Unlock()
  2731  	if es.closed {
  2732  		return nil
  2733  	}
  2734  	es.closed = true
  2735  	if es.earlyCloseFn != nil && es.rerr != io.EOF {
  2736  		return es.earlyCloseFn()
  2737  	}
  2738  	err := es.body.Close()
  2739  	return es.condfn(err)
  2740  }
  2741  
  2742  // caller must hold es.mu.
  2743  func (es *bodyEOFSignal) condfn(err error) error {
  2744  	if es.fn == nil {
  2745  		return err
  2746  	}
  2747  	err = es.fn(err)
  2748  	es.fn = nil
  2749  	return err
  2750  }
  2751  
  2752  // gzipReader wraps a response body so it can lazily
  2753  // call gzip.NewReader on the first call to Read
  2754  type gzipReader struct {
  2755  	_    incomparable
  2756  	body *bodyEOFSignal // underlying HTTP/1 response body framing
  2757  	zr   *gzip.Reader   // lazily-initialized gzip reader
  2758  	zerr error          // any error from gzip.NewReader; sticky
  2759  }
  2760  
  2761  func (gz *gzipReader) Read(p []byte) (n int, err error) {
  2762  	if gz.zr == nil {
  2763  		if gz.zerr == nil {
  2764  			gz.zr, gz.zerr = gzip.NewReader(gz.body)
  2765  		}
  2766  		if gz.zerr != nil {
  2767  			return 0, gz.zerr
  2768  		}
  2769  	}
  2770  
  2771  	gz.body.mu.Lock()
  2772  	if gz.body.closed {
  2773  		err = errReadOnClosedResBody
  2774  	}
  2775  	gz.body.mu.Unlock()
  2776  
  2777  	if err != nil {
  2778  		return 0, err
  2779  	}
  2780  	return gz.zr.Read(p)
  2781  }
  2782  
  2783  func (gz *gzipReader) Close() error {
  2784  	return gz.body.Close()
  2785  }
  2786  
  2787  type tlsHandshakeTimeoutError struct{}
  2788  
  2789  func (tlsHandshakeTimeoutError) Timeout() bool   { return true }
  2790  func (tlsHandshakeTimeoutError) Temporary() bool { return true }
  2791  func (tlsHandshakeTimeoutError) Error() string   { return "net/http: TLS handshake timeout" }
  2792  
  2793  // fakeLocker is a sync.Locker which does nothing. It's used to guard
  2794  // test-only fields when not under test, to avoid runtime atomic
  2795  // overhead.
  2796  type fakeLocker struct{}
  2797  
  2798  func (fakeLocker) Lock()   {}
  2799  func (fakeLocker) Unlock() {}
  2800  
  2801  // cloneTLSConfig returns a shallow clone of cfg, or a new zero tls.Config if
  2802  // cfg is nil. This is safe to call even if cfg is in active use by a TLS
  2803  // client or server.
  2804  func cloneTLSConfig(cfg *tls.Config) *tls.Config {
  2805  	if cfg == nil {
  2806  		return &tls.Config{}
  2807  	}
  2808  	return cfg.Clone()
  2809  }
  2810  
  2811  type connLRU struct {
  2812  	ll *list.List // list.Element.Value type is of *persistConn
  2813  	m  map[*persistConn]*list.Element
  2814  }
  2815  
  2816  // add adds pc to the head of the linked list.
  2817  func (cl *connLRU) add(pc *persistConn) {
  2818  	if cl.ll == nil {
  2819  		cl.ll = list.New()
  2820  		cl.m = make(map[*persistConn]*list.Element)
  2821  	}
  2822  	ele := cl.ll.PushFront(pc)
  2823  	if _, ok := cl.m[pc]; ok {
  2824  		panic("persistConn was already in LRU")
  2825  	}
  2826  	cl.m[pc] = ele
  2827  }
  2828  
  2829  func (cl *connLRU) removeOldest() *persistConn {
  2830  	ele := cl.ll.Back()
  2831  	pc := ele.Value.(*persistConn)
  2832  	cl.ll.Remove(ele)
  2833  	delete(cl.m, pc)
  2834  	return pc
  2835  }
  2836  
  2837  // remove removes pc from cl.
  2838  func (cl *connLRU) remove(pc *persistConn) {
  2839  	if ele, ok := cl.m[pc]; ok {
  2840  		cl.ll.Remove(ele)
  2841  		delete(cl.m, pc)
  2842  	}
  2843  }
  2844  
  2845  // len returns the number of items in the cache.
  2846  func (cl *connLRU) len() int {
  2847  	return len(cl.m)
  2848  }
  2849  

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